Seeing that she is 17 (when she turns 18, you have no say because that's when they are on their own) I would say bring him to court, if you can get any evidence that he is an unfit parent, do so. Otherwise yes, contact the police. If you know when and where he is having these booze parties, contact the police and give them a tip that you know there is underage drinking going on at given address. Police will go and investigate, and your ex may get into some serious trouble.(Fines, court, etc) Do this all on the DL.

It is illegal it doesn't matter if she is 18 or not in ALL US States to give a minor alcohol. For that HE can go to jail .. my STBX has major issues with drinking all documented .. his ass in jail end.of.story. I DO NOT play when it comes to drugs and alcohol .. for a parent to physically harm a child (you will need a definition of child I do believe that the fact she's an underage drinker trumps this issue)the reality is NO alcohol .. period. The idea that he is setting his daughter up to have issues with alcohol is a big red flag .. some education for her about the life long effects of addiction on her body (especially as a cancer survivor) it sounds like there are other issues going on. Good luck and big hugs .. this is a tough situation.