That is definitely a very valid theory. The big thing that speaks for Vinny or a traitor, on his behalf or not, is the camera. If Derek's assumption, that it couldn't have been installed during a party, is correct, then it would have to have been someone with completely free access to the mansion - so basically a DIK, or a former DIK. The feminists would have a hard time installing it, and I don't think Jamie is retarded enough to unknowingly install one.
But maybe Derek is wrong, who knows.
Concerning Vinny's motivation: one event we know basically nothing about is how he left B&R and the DIKs. Of course, it could have just been him realising that a career in academics wasn't for him and that he would rather pursue one as a narcotics supplier, and he just left with a smile on his face and firm handshakes all around. But since we know that he is a piece of filth with acute micropenis syndrome and an even shorter fuse, I think it is not too outlandish to assume that something more happened and that he holds some kind of grudge. It could maybe even be something that appears so minor to the others, that nobody even realises that he holds a grudge.
I think it's also absolutely possible that there is more than one party at work. The camera stuff, the Cathy picture, the Hell Week pictures - we don't KNOW that it is the same party behind all of that.
Whoever is the culprit, I think it is safe to assume though that Beth is just a tool and definitely not the brain behind anything. During the final conversation of bullshit class she seems to be dumb as a rock. And because of that, I think it is very possible that we won't get much further in uncovering this business in Ep. 11. When confronting Beth, we might simply learn that she does it for money she gets from some anonymous source and that she desperately needs because her dog has AIDS or something, which is also the reason why she works in the cafeteria. We will see.