As both chapter adviser and attorney, I certainly wear two hats and have different sets of ethical responsibilities. I represent the chapter, not the individual brothers, but I really do have some interesting obligations when it comes to privilege. I also have additional protection, I think, from ever being considered a mandatory reporter since I haven't cashed a paycheck from my alma mater in about 13 years and the whole attorney-client privilege thing.
And tangent: Having a lawyer as an adviser can be a blessing and a curse, as lawyers, we can be tempted to overplay our hand being used to concepts like "beyond a reasonable doubt" when you're playing by a totally different set of rules in the halls of academia. The Tennessee PKA butt chugging press conference comes to mind when I think of lawyer-advisers overstepping.
https://www.youtube.com/watch?v=keTbsSfMOdI
/tangent
I would consider myself bound to obtain some sort of authorization (definitely in writing) from the chapter's President or whatever entity might be required [note to self, figure this out, this seems important] before disclosing an suspected incident to the University.
I will tell you this is all very new and when you go into one of these things thinking you have researched the rules, know the student Code of Conduct better than anyone, often your initial assumptions evaporate very quickly. At this stage though, barring experiencing some sort of crippling sanction (note: I've never been part of any Title IX process where any party has been found to be responsible for sexual misconduct), I'm pretty much okay with feeling like I'm engaging in a game of Calvin Ball with the University. Things will eventually start to calcify as administrators become comfortable with processes and procedures.