Here's a 10-year old thread on the subject.
http://www.greekchat.com/gcforums/ar...p/t-17203.html
No one then could point to a specific rule forbidding this. 10 years is a long time though and rules could have been amended. If you can quietly and discretely get ahold of the rules and determine whether or not anything wrong happened here that's fine. I imagine your research will likely lead to the conclusion that it's not specifically proscribed, but it looks icky (for lack of a better word). If that's all you've got, your campus could probably do without some sort of a scandal. If your research reveals that there is a problem, I certainly would bring the issue to your adviser so that she might first have the opportunity to address it in a constructive manner.
If you decide to make this a confrontational affair, you may very well alienate the administration and consider the rest of your term wasted in terms of any ability you're going to have to accomplish any sort of agenda.
I could only tell you how to deal with this within an NIC group and specifically my NIC group only. In Sigma Nu, our Law states at Art. 4, Section 2.2 "NO DUAL MEMBERSHIP. No Chapter shall elect or initiate into the FRATERNITY any member or former member of a General College Fraternity, except as provided by this Article." (The Article doesn't have anything further which is of any help).
If it came to my attention that we had this issue and we were dealing with an alumnus who had graduated more than 2 years ago, I'd have to first go to the High Council (or national governing board) and file a complaint there. Assuming the High Council approved the filing of the complaint, I'd have to then give the Defendant notice (there are procedures for that) and a trial would be commenced wherein the active chapter would be the jury. The only question before the body would be whether the Defendant is a member of more than one general college fraternity, once a verdict is given, this can be appealed to the High Council and then to our Grand Chapter (our national convention). I left a lot of details out, but you get the idea. In Sigma Nu, such grey areas are decided by collegiate chapters and then are subject to appeal. It's a potentially nasty and confrontational process. I've been through it a couple of times. Not pleasant in the least.
Know your facts before proceeding. If there's any grey area, I'd leave it alone.