Exactly and this makes the casinos a win win situation because not only they are gonna win in the long run, in long run, Bitcoin prices may double or even reach moon, and that can easily make the casino owners billionaires 
They have a double chance to increase their money as they can win and increase their btc and increase its value at the same time in the future.
However, I think they are also employing a risk management program to to avoid volatility on the portion of their coins they are holding, they maybe from time to time convert it to stable coin so the business would really last long.
What we are thinking is the positive scenario only, what if BTC will drop 10x and that would hurt the bankroll of the gambling sites as gamblers are still gambling based on its fiat value although they are using btc as a tool to gamble.