My campus's chapter of Sigma Nu did a joint event with ODU-Out (a GLBT student organization) that brought in guest speaker Shane Windmeyer.
He gave a very informative presentation on how to promote tollerance and acceptance within the Greek community on one's campus, and he might shed some insight on Out-Friendly organizations.
I know within my college's chapter of my fraternity, we have brothers from all walks of life... straight, bisexual, gay (openly and others privately), and every ethnic and religious background you can think of. We embrace our diversity, and it has become our strength in recent months.
My reccomendation would be to explore this website and see if Shane offers any insight, and if not, approach Sigma Nu, as I know (from my experience as a brother) that our values encourage being true to oneself.
http://www.lambda10.org/outgreek/
Good luck to you!
-JCA