....So if you have sent them BTC and its still pending .. then you decided to send some ETH.. you won't be able to make a withdraw since you have a pending BTC transaction.
Maybe this matter has nothing to do with the different blockchains as you are claiming or not about pending tx. You deposited BTC and wanted to withdraw in ETH but did you even meet any of their wagering requirement? It looks to me that you are only trying to use the casino to as an instant exchange.