People who apply for reality shows arent generally "actors" (although some are) but they do all crave attention, so they may have done a commercial, or some other acting gig in the past.
I know for survivor, they have to follow strict game show regulations.
As for apprentice, when you have a ton of applicants, you can pick the cream of the crop of personalities.
All fake? No way, imagine if proof leaked out, how many careers would be destroyed, especially mark burnetts.