There is actually a big difference if the casino has no restriction on withdrawals of someone which deposit/s is unconfirmed. Imagine if a player wins with their unconfirmed transaction, and they'd be able to freely withdraw said winnings. This player could also try to double spend the same UTXO with a much higher fee so it will likely confirm first making the previous transaction invalid.
I don’t think that’s possible. Back in the early days of casinos and sportsbooks, I experienced them crediting my deposit right away as long as it was already on the blockchain. But they wouldn’t process the withdrawal unless it had at least one confirmation, which I believe is just a standard security measure.
The only downside for them is if the bet loses, the gambler could try to double-spend it by sending the same funds to another wallet. That way, the balance wouldn’t actually reach the casino’s wallet, which is a sneaky way of cheating on the gambler’s side.