Apart from the competition so far there has been no casino token that has impressed its performance so that it can attract many people to invest in it, even some casino tokens that can be said to be famous have trading volumes that are also very small compared to the coins that many casinos use as their means of payment, so if some casino put it in maybe not many will play with the token because there is a fear that it will be difficult to sell it because of the low trading volume.
I don't know much, but when I was playing in bitcasino using the BTC rewards, they converted the coins to USD while playing the slots. They were always adding and subtracting the winnings and losings respectively in the uBTC. The numbers may seems dollar but they are just numbers. If I am not wrong then in duelbits, they have a default coin which is equivalent to USD which means whatever coin you deposit it converts to their native coin. When you withdraw it again converts the native coin to your desire crypto.
None of these coins or USD points are traded in blockchain. They have no blockchain existence I guess.