When I was a kid, my grandfather used to go to the horse races with his best friend who was a priest almost daily. So while there may not be anything wrong with a priest gambling, it is a bit unusual in the fact that it isn't something you see everyday, and in that respect may drawl more attention than provide cover. Especially if the preist is the 'big bettor'. By my way of thinking anything out of the ordinary is bad, as I try to blend in.
As for Jack Black's "gay cover". You might be surprised.

I have used this tactic effectively a many of times. It would look extra bad if a casino were to throw out a feminine 'gay acting' player. Right or wrong, that's the politically correct climate we live in, and I beleive it will buy you a little extra slack. There is a pretty well known pro, who recently came out with a book, that I have spoken to about just this topic. He used 'the gay act' in the past and also believes it to buy cover. Since, our discussion was private, I won't go any further than that. If he wants to chime in, he can. lol
Well, it looks like the 'gay cover comments' I referenced, were removed either by the poster or mods.