I can see some flames coming, but thought I'd give an answer before they start
Just from experience - staffing on ships is very fluid. Who's on this month may not necessarily be there in 2 or 6 months or next year, so it would be hard to book a cruise a year out and get the staff you wanted. Entertainers change on a per cruise basis, cast on a 5 to 8 month contracts.
(For the benefit of others reading, companies like Atlantic and RSVP will charter an entire ship. With those groups, the cruise line specifically schedules the FOD staff for the duration.)
Have you spoken directly to the cruise lines groups and charter reps? What do they say? I would think if you're booking in a group of any size, they'd be able to advise you.
However, what you're asking seems to be the equivalent of walking into a hotel or resort and asking 'who's gay here' . . . would you do this in that situation?
The line I work for does have a community bulletin board where both FOD and other groups like vetrans or Friends of Bill W have meetings posted every cruise. I have known a few of the cast to check out the meetings. . . .