I don't see how it would not count as a direct connection.
Looking at the rules for direct connections, page 232:
Devices have a universal data connector, which is the global standard for connecting devices together for power and data exchange. If you have a cable, you can connect to the device directly. Cyberdecks and datajacks come with a meter of built-in retractable microfilament data cable, or you can always buy a cable for about five nuyen per meter (some devices, especially those installed in buildings, are connected by cables to mitigate noise). When you use a direct connection, you ignore all noise modifiers and modifiers due to being on different grids or the public grid. It’s just you and the device.
OK, so cyberdecks and datajacks come with built-in data cables, and all devices (including throwbacks) have universal data connectors.
Looking at the rules for personas, first on the description of it on page 218:
A persona is more or less what it sounds like: a person in the Matrix. A persona is the combination of a user and a device that gets the user onto the Matrix. The fact that the device has a user overrides the device’s normal icon status, turning it into a persona. A persona is usually based on a commlink, cyberdeck, or rigged vehicle or drone, although technomancers are a sort of device-less persona.
All right, we know that once a hacker (decker or technomancer) interfaces with the Matrix he becomes a persona, and that said persona is either based on a device (decker) or not (technomancer).
Further on, actual rules for devices and personas, page 234:
A device in the Matrix is any wireless device in the real world.
When a person uses a device to connect to the Matrix, the device’s icon is subsumed by the persona’s icon, so it’s basically gone from the Matrix until the persona jacks out. You can only run one persona at a time; switching requires you to reboot both the device you’re currently on and the device to which you want to shift your persona.
Finally, about icons, from page 216:
icon:The virtual representation of a device, persona, file, or host in the Matrix
Bear with me, all of the above lays the foundation for the next part.
From the Brute Force and Hack On The Fly descriptions, page 238 and 240, respectively:
You can use this action to mark a target without obtaining the normal permissions you need. <znip> If you succeed in this action, you place one mark on it.
You can use this action to mark a target without getting the normal permissions. <znip> When targeting an icon, you put one mark on it, up to a maximum of three marks per icon.
Note that Brute Force doesn't actually spell out that the target is an Icon, which could be problematic if you want to rules lawyer this debate all the way to hell.
Ok, so we know that every device connected to the matrix shows up as icons in the matrix (leaving aside display filters for now), and we know that when a hacker interfaces with the matrix their device icon is supplanted by their persona. The persona of a hacker can take actions against icons, such as another device, for example a commlink or cyberdeck. We also know that a device can be directly connected to another device through universal data connectors.
This is where the gray area appears. Nothing in the rules state how the direct connection works; the relevant section only states "It’s just you and the device." In my opinion, it is safe to assume that if a decker can connect his deck to a universal data connector on another device and interface with said device when his persona is on his deck, he can also wirelessly connect to his deck from a second deck and perform the same action.
The matrix actions make no distinction between whether or not a device is directly or wirelessly connected; they simply state that the target/icon, and this is important, is marked if you succeed in your Brute Force/Hack On The Fly action. Since the target HAS to be an icon with the whole "everything on the Matrix is an icon" definition, it logically follows that if a device is directly connected to another device where one of them is wireless, then:
a) the wireless device can be accessed as normal by it's owner (example, a cyberdeck)
b) the wired device can be access by a persona on the wireless device (as described in the direct connections section)
c) the wireless device is vulnerable to hacking by a third party (or by someone inviting marks on it)
Since personas do not reside on the device they are hacking in SR5 (unlike in SR4 where the persona entered the node), the persona just needs to be able to access the wireless device in order to meet the requirement to have a direct connection to the wired device on the other end. No other explanation makes sense to me, as hackers by definition "breaks the rules of the matrix". If you can't plug a wireless device into a non-wireless device and then hack the wireless device, there's something wrong with the system. Directly connecting to a device doesn't automagically make the entire matrix disappear and leave "just you and the device", it just means that until you make that direct connection you will not see a non-wireless device as an icon and you will be affected by noise. Once the connection is made, however, noise is no longer an issue and the icon of both devices is likely to be equally bright.
As I've described, nothing in the rules specifically prevents or allows this type of connection. However, in the example above, the wired device simply wouldn't show up in the matrix for anyone not connected to the device that had a wired connection to it. Once the owner/hacker connected to the wireless device that was connected to the wired device, though, the wired device should show up as an icon in the matrix, and thus be ripe for the picking, so to speak.
Rules-lawyer all you want, to me this is the only thing that makes sense and the way I would play it.
TL;DR
To my mind, a decker/technomancer could attach a wireless device (commlink, cyberdeck, even a datatap as long as it's wireless is switched on (and preferably running silent)) to a non-wireless device's universal data connector, hack or access said wireless icon and then see the wired device as an icon on the matrix, thus making it a viable target.
[EDIT]
Lynchpin to my argument:
1. A hacker, such as the one in the example on page 224, attaches his cyberdeck to a maglock slaved to a host, establishing a direct connection between the the maglock and the deck
2. The hacker, successfully gaining a mark on the maglock, also gains a mark on the device's master; a host, which is by definition a wireless non-physical entity
3. The description of PANs and WANs state that devices in a WAN count as directly connected, implying that wirelessly connected devices can also benefit from direct conenctions, at least in some cases
4. This is also supported by the fact that devices in a PAN are vulnerable to the same direct connection hack as above, and gaining a mark on a directly connected device that is a member of a PAN also results in a mark on the Master device (though it is not stated on way or another if the benefits of a PAN can be extended to a device that is directly connected to another member)