I would be surprised if Vaughn set-up the rape. That would be some diabolical ****, and they seem to be playing him as a good guy at this point. There would be no gray if they go that direction, he'd be completely hated.
The more likely "twist" in my opinion, is the guy he tipped him off to is just some guy he wanted whacked and not the rapist.
I wouldn't be surprised, however, if that was really the guy. I also wouldn't be surprised if there was no blackmailing at all by Vaughn. He seems to be the type who tries to make sure everybody is happy and everybody wins, not the type to pressure his own crew through intimidation tactics. His comment about "everybody getting touched" makes me think any dastardly deeds performed by the cop on behalf of Vaughn were done after the cop came to Vaughn and asked him for a job, or for help in exchange for a job, most likely when his wife leaves him and probably sends him on a binger.