Cait said she was in the city, not in the Black Guild Hall. I know she was trying to talk to Azga but was so nondescript that Reap didn't pick up on it.  Static Flash mentioned meeting with Nies, but he didn't specify meeting her in the Black Guild Hall either. So as far as I can tell, neither of them are in the Black Guild hall, just the Black City in general (And that could be anywhere). 

Right now the only people in the Black Guild Hall is Azga and Arms Slave. If anyone else shows up, they'd have to take the effort to go in there themselves.