Yes, currently BTC and BUSD do not supported for withdraws, but we are providing swap utility of BTC and BUSD to (USDT, USDC) which are supported for withdraw
This is good feature on a casino. What exchange rate you are using and does your swap feature has a exchange fee because this will surely be disadvantageous your user. Why not automatically convert all the deposits to USD then allow then to withdraw on any currency that you support without the need to swap or something.
Duelbits has this kind of feature that automatically convert deposits to USD coins then user can withdraw on their desired currency directly on the withdrawal tab.