Tommy's not the rat. He even asks the dormies and Quinn to look around for suspects. And Rusty's definitely not it - he could simply disband the frat if he wants it to fall. Plus he's in the pictures.
My best guess is DPC's going to build a freeroam to get statements from the boys, the preps, and the dormies, and then make them slowly close it down to target one specific DIK - probably Nick - and force players to accuse/abstain/defend during a discussion/trial. Idk if Nick's going to be excommunicated, or put on probation, but I think voting out a brother in Ep11 would be too soon, and should only be done when the boys actually find the culprit(s) and get confessions. Either way it's a mess with how little we actually know, but Nick's been the red herring since ever, so he's probably innocent. I think Beth is just a pawn, and even though she may have been the one to take Cathy's nude, someone else is in charge of the operation. The Halloween photos are probably coming in handy soon for the boys to shift through the suspect list.
Also, when the jocks talk about the photos, Anthony points out to Chad it's not MC. Yet later on Ashley says Anthony believes it's MC, and she trusts Anthony. There's definitely something fishy in his statements. If 11 shows more of the jocks, there might be sth to be revealed, and the real culprit(s) might be found in 12, closing the season.