As for the fraternity they are up $h1t creek. They deserve to be there. Many states require you have a license/permit to sell alcohol. If that's the case in Massachusetts I can see why the Health Department would intervene. They're probably the body that controls issues like that. As far as the charges against you and other students get together and hire an attorney. If ya'll pay together it won't cost that much and probably just the act of doing that will scare the administration back into sanity.
Or maybe not. I've heard stories about how crazy UMASS administration is when it comes to punishing people for having fun
What the law folks are telling you about "Burden of Proof" would be correct in the American judicial system. But remember, this is the school judicial system. It doesn't even pretend to be fair. It's a question of who's been able to pack the courts. I'd suggest that in the future Greek organizations in general might want to use their leadership to secure a majority on the Student Supreme Court (if you have one).
As I've said before in my personal dealings with the Student Supreme Court at Central Oklahoma I've recieved some nutty rulings. A great example of on said that my committee (the judiciary -- we approve presidential nominations before the senate gets to vote on them) was taking longer than the president liked to confirm his nomination for VP. They cited (and took way out of context) SENATE RULES in their ruling (out of their jurisdiction) and then stated that my committee had a deadline in getting the nomination through (can you say violation of separation of powers?). There were parts of the ruling that directly contradicted others.. it was great.
I just give that example to say that I know how inane student courts can seem at times. Get yourself an attorney and go after the school in *real* courts.