Yes. All transactions on the blockchain network are subject to transaction fees. And Tether is no exception. So expect a small deduction for each transaction you make. However, the emphasis is on small, as USDT is known for having lower fees than others.
This applies to transactions that are trades as much as casino deposits, so keep that in mind.
If this is something you don’t like, there is little you can do about it. The casino is not responsible for blockchain policy. It is between you and your wallet service. That being said, beyond the inevitable blockchain fees, a good operator will not tack on any other costs. So if you do see such a thing, we would say it is time to make a different choice.
As for how to determine those transaction fees, from our experience, good operators are transparent about all network transaction fees too. Many show them in full detail under each payment method, both when you go to deposit and to withdraw. You can also check under the casino’s FAQ section, or contact customer support which should be able to provide these details as well.