Serious question: if an accelerator asks participating startups to not hire employees from one another, does it violate laws governing fair competition?
Even if it isn't illegal, it's probably contrary to the interests of the accelerator: if one of your startups needs somebody more than another--enough for an increase of pay or some other benefits--then, for the whole program, having that person move is probably better than artificially forcing him to stay.
I think that would fall under conspiracy to commit crimes, but talk to a lawyer. In the end, I think it would show that the accelerator was pretty stupid. There will be a natural inclination not to do so inside the program anyway, so why cross the line like that?