I'm not sure how can withdrawal fee paid by the casino can be abused, would you mind to tell a bit more about what you are talking about?
Every time I make a blockchain transaction that leaves behind a tiny amount of change (say, a few hundred sats), I can send that change not to my own address, but to an address provided by the casino.
Then I just place one smallest low-risk bet to meet the wagering requirement - and now I can withdraw the consolidated amount as a single coin.