This is an exercise in hair splitting. I can't speak for any other
group besides Sigma Nu, but I swore during ritual never to join
another fraternity. Would you support someone in violating the oath
they took in another org's initiation ritual?
This is part of the reason we sometimes make a big deal about saying
that non-social GLO's are *not* fraternities. I can join an honor
society or a service organization, or a professional-interest group
that happens to have Greek Letters and an initiation ceremony. But to
say I can quit Sigma Nu and join Omega Psi Phi is NOT THE SAME
THING!!!
This is not a subtle point about which conference the GLO is in. It
is common sense.
BUT... There's still one question I don't know about... If I quit my
NIC fraternity and get a sex change, can I join an NPC sorority?