I'm not a constitutional lawyer and I doubt any of these administrators you spoke to are either if they said that to you. Private colleges have always been able to manuever through federal acts like this if they don't depend on the government for funding. But any public institution or university must comply with this and HR 6 (the '98 amendments to the Education Act). As for using it as leverage to make us co-ed, I cannot see how that could be possible. The act specifically protects fraternities and sororities, as well as other single-sex organizations.
If you want to read through the act yourself, it's here :
http://www.usdoj.gov/crt/cor/tlix.htm
AXPAlum