You might see him, but not know much about him at first. It all depends on how big the campus is and how sociable many of the students are.
Honestly, given their notoriety and number of enemies it's a wonder there aren't more people reporting the DIK parties for drug and alcohol usage. That's what makes me think this may have been a random one-off - if somebody is trying to get at the DIKs, they almost certainly would've done so sooner.
Sure, it could be Nick, but that seems like a pretty stupid move from him; if a former member goes to the faculty and reports their activities, it's gonna be pretty obvious how he knows about them and he'd be punished too. It could be part of Magnar's long con, but it seems like kind of a risky move to report them to staff in a way that could get them shut down before your killing stroke is ready. It could be the dorm girls, but if this was something they could've done from the beginning do you really think they would've waited so long to at least file a report? It could be the alphas, or maybe even Tybalt, but they drink on campus too.
Plus, Philip's laid-back demeanor about it all leads me to think the report wasn't a high concern. I'm sure the DIKs' reputation is well known even among the faculty, but he didn't seem all that interested in busting them over something that was very obviously true. It makes me think whoever filed the report can't have pushed too strenuously for it to be investigated.