"The "God hates fags" is not legitimate Christianity. Phelps is a lawyer, every member of his "church" - who also happen to be his family members - are all lawyers. He's either a regular nutcase or a closet leftist nutcase. But actual Christian who represents a lof of actual Christians? No way.
I wonder what other kinds of groups are allowed or disallowed for RAs at either this school or other schools. Are they allowed meetings of other kinds in their rooms?"
Of course it's not. Yet, there are many Christians who simply have no qualms about telling homosexuals that they're going straight to Hell. Some post here.
Obviously, that would be incompatible with being an RA in a public university. It's not the RAs job to bring religion to the students, frankly.
As for meetings of other kinds, I suspect that it's only religious stuff that is prohibited. Why? Because religion is so often a separater of people. Think about it. There may be many who dislike your particular religious beliefs, and who won't feel at all shy in telling you so. That's not really the function of a Resident Assistant in a dorm, it seems to me.
Phelps is definitely a nutcase: he has been a longtime admirer of Albert Arnold Gore, Jr., hasn't he?