If I was holding some really dodgy bitcoins there is no way I would trust a casino to launder them. If you deposit 1000 BTC and then gamble until you lose 50 BTC, the 950 BTC that you get back could be exactly the same 950 BTC you started with minus the 50 BTC. How do you know that your player funds are betting mixed up with the other players. You can't be sure so it would be too risky in my opinion.