Truth be told, I've never been to a real casino
I mean a real one, not some room with slot machines and similar stuff. But from what I know (okay, from what I've seen in the movies) people don't use cash there directly. Casinos use gaming chips, i.e. small discs used instead of paper money and coins. Then you can redeem the chips (provided you have any left, of course) for real cash. To me, Bitcoin would be cumbersome to exchange these chips for in these circumstances
And there are also some people who use some online games to gamble and have fun for example tongits go and other kinds of apps too
OP asks about real casinos (think Las Vegas here)
For this, it is necessary that the casino accept cryptocurrency as a payment for chips.
I believe that there is no problem. Now, nothing prevents you from exchanging chips for dollars, and then buying cryptocurrency.