Xenon is right in that the Social skills won't help against IC. Mechanically, IC makes Matrix Perception tests. See the sidebar on pg. 235 regarding the sorts of things IC can learn by inspecting your icon. The last action you performed (if it was illegal) and programs you're actively running can tip the Host off that you're probably a Hacker, although in certain contexts other things may also be suspicious (maybe the IC notices that your commcode is Hackerman3000@Shadohack.horizon and that really doesn't look like what the company employees' commcodes would look like, even though you made your Persona Icon conform with employee Icon standards..)
However, social skills ARE absolutely useable on Spiders: they're people too, afterall. And technically, you can't even tell the difference between IC and a Spider until you inspect their Persona anyway and ask that question on a Matrix Perception test.
All that being said, hackers have ABSOLUTELY good reasons to take Disguise/Con/etc. If you know anything about real life hacking, the primary skill in most hacking is social engineering. You talk to authorized users, get them to give you their legit credentials, and you use them. In game terms, tricking an employee to give you their credentials (or, lol, finding them written down on a sticky inside their desk) essentially replaces the Hack on the Fly/Brute Force stage of the hack: You just log in as the employee, gaining however many Mark(s) the employee is supposed to have (probably just the 1). Even better, you'll also already have whatever marks on files/devices the employee would have. You can also use social engineering to find out passcodes the employee uses to bypass File Protection.