You have implication of cyberware in Starcraft 2 (if I can remember, I don't like Activision), but it's not unlikely for it to exist a long ways back through or even before Starcraft 1 if you want your campaign to start back that far. Raynor was mentioned to be a marshal with power over a variety of people, so it's not implausible that people like him would be tasking bounty-hunters to go out and snag deserters, misbehaving scientists, investigate unregistered research bunkers, etc. Quite a lot of mystery/horror-element options if you're wanting to play a game like that, though sooner or sooner the Zerg would become something you have to deal with, and you'd have to decide if they're the scary monsters portrayed in the cinematics or the easily blown-apart mooks portrayed in-game.
Against sheeple, a Zergling is bad by itself. Against a trained shooter and such, Zergling would need to get a drop on them.
It's when you have multiple Zerglings and larger bugs that become an issue.
As far as cyberware, I am viewing it as low key stuff, just enough to help out the trained users or those who are sick or injured. Depending on where the group starts, it may or may not be too prevelant, and can even be subject to various norms.
Exempla #1: A farmer on Mar Sara might have a cyber arm/leg due to injuries and such, he probably won't have a cranial implant with access to the network.
Example #2: A research scientist/professor on Tyrador will have a cranial and eye implants to access his notes and diagrams for his studies and projects, though probably won't have any limbs replaced (unless there was a really interesting story behind it).
Basically, I mostly see low end cybernetics being in use by the majority, with those either lucky or with access getting better gear (depending on location, most might have a claw cybernetic if they lost a hand, with some getting a better model. Your mileage may vary, depending on location).
As for James, it would depend on the timing. Terran Campaign of SC wold probably be under the Magistrate and such.