As mentioned above if the poker site views an American Express deposit as a cash advance you will likely pay a higher interest rate and fees for it. You are also subject to your own personal AmEx credit limit and must make your minimum payments to keep your card active. It’s not very likely you’ll be able to process a poker site withdrawal to your AmEx card. On the upside, though, most poker sites have waived any extra fees for depositing with your American Express card.