Streamers work for money. If he get not enough money from stream - he get them from company. He can use money that he get due to contract, possible that casino gives him some money for gambling but i can`t call it "fake money" if he win - he got real money. How did he get it - it is another question and it isn`t about "fake money" as for me.
Or he use his referrals' income to gamble. Since there are million of subscribers and even more views, I believe he must make a huge amount of money reffering gamblers to casinos. In the end he uses this money to gamble on his videos without risking money from his own pocket. It's more like "free money" than "fake money". It's just a possibility, though. We can't confirm anything, because all the informations at our reach are purely speculative.