In fact, these are highly recommended due to the low cost and speed of the transactions. All casinos operate on the account system - you send them money and your account is credited for that amount. As you gamble, money is credited or debited as you win or lose. Many operations now allow you to have money withdrawn directly placed back onto the credit card that you first deposited money into your account with. This option is recommended as you can access your winnings within days.
Casinos charge reasonable fees for other withdrawal options.