Special NPC traits can only be accessed if you hire them as staff, not as pornstars.
The Cougar - location: bar. Grants "cream machine" trait to MC that allows you spunk as many times as your want in a shoot (this does not affect quality or anything). The real perk she gives is leveling up your model's sex skill with every performance at no extra charge.
The Fitness Instructor - location: gym. Raises model's fitness stat as they work.
The Maid - location: hotel room. Grants free make-up changes (<- personally, this seems weak so using her as a pornstar is no big loss to the MC - hopefully this will change to a beauty stat boost like the other girls do.)
The Nerd - location: library. Her perk drops the pay of other PAs by 5%. Again, this seems kind of weak (an intelligence boost like the others would make more sense)
The Trophy Wife - location: hotel lobby, only on Sat & Sun. Unlocks the jewelry store at the mall, which once you visit it will unlock jewelry options for your models. In future builds it has been hinted that she will unlock other locations, too.
The Nurse - location: hospital, 12mid-6am. Gives you free STD pills and cuts all rehab times in half. This is very valuable, so you should always take the option to hire her as a medical advisor.
The Punk - location: beach. 1st encounter is random but you need a certain number of fans for later encounters. Acts as a boosted marketing PA, which means extra $$$. She also unlocks the tattoo parlor at the mall. Visit it once and you now have tattoo options.
The Cops - location: 1st encounter at your office, 2nd in the park, 3rd in the alleyway when you try buy drugs. Yes, you can recruit them! They both have security related perks and thus make good security guards. Between the two of them you probably won't need any more security at all, in fact.
I must repeat this: You do not get any of their special bonuses if you hire them as regular models/porn stars. They must be hired as personal assistants/specialists to get their unique benefits.