The Casinos would love it if you could plug your ATM card right into a slot machine or give it to the pit boss. Unfortunately, for them, it's currently illegal in Nevada. I think so would getting chips directly from an ATM.
Nevada insists you get the money and give it to the casino directly so that it's known not be be a bank or credit card loan, which may not be collectible once you leave the state.

Checks are different at the cashier. They are assumed to be cash instruments. That's the theory, and it's a felony to bounce a check but not to default on a loan.