Responses
Mate, okama was derogatory, much like the word queer was years back. Now, it's become your standard umbrella term for drag queens, effeminate men, gay men, and what not (much like onabe and I forgot that other term is gaining traction). You have a point that it's generational, but in this case I'm pretty sure in his context it was for drag queens. After all, he worked there.
I'll admit that I got a little pissed when I read him saying "Okama Bar", since okama is a kind of like "fagg0t", it's a slur to call gay men and/or drag queens(or trans women even), since they are the same thing to most japanese people, and as a queer person that generalization really pisses me off. But I know this whole manga was a hot mess, and since they're from an older generation it'd make sense for them to know the word Okama more than Gay.
(still pissed about the representation the gay bar had though, it was ridiculized in a kind of insulting way, but I know I have to let it go too)