There are already a few gambling sites where you can actually gamble
with USDT (e.g. luckygames.io offers this possibility).

However, I´d be careful what you wish for. USDT is completely centralized and
the operator can freeze your funds anytime. There is at least one
precedent where they did actually freeze 30M USDT.

One of the big advantages of Bitcoin is that no one can freeze your funds and
you can gamble from anywhere in the world. Some sites may restrict IPs from
certain countries, but this restriction is not on the protocol layer of Bitcoin.
To sum up, I´d stick to gambling with BTC and I wouldn´t touch Tether with
a ten-foot pole.