It is not clear so Stephen Burke is involved in the restaurant or sex for school money. These are guesses that came from hints in the game. Therefore, it cannot be ruled out, but these clues are not concrete enough for it to be considered certain for Stephen to have anything to do with the restaurant or sex for scholarship.
Stephen Burke admits so he puts students in touch with investors, I agree. But that's nothing illegal and doesn't prove so that he arranges female students scholarships for sex. More likely is so that these girls approached investors and thus hooked up with a sugar daddy. Then when several girls have done this, rumors start.
In EP4, Quinn told Riona that Melanie and Sarah did it. What did they make? In EP8, Sarah said to Melanie so Sage would think they were sluts anyway. Why? To me, it presented itself as follows. Melanie and Sarah were two students who got such an investor as a sugar daddy. These investors paid for their studies in full. Melanie and Sarah are HOTs and Sage is their president. Sage found out, thinks they are sluts because of it, and told their father. As a result, Stephen Burke probably even stopped it all himself, but couldn't take any further action against it because the reputational damage it would have caused would have affected several rich people (Royce, Burgmeister, Burke and the investors). That's why Sarah and Melanie are still in college, so they don't take it public.
Quinn and her restaurant are trying to do the same thing as Melanie and Sarah. Only Quinn doesn't have the connections like Stephen Burke and is trying to do it through the back door by sticking to the preps and building those connections through the restaurant.