Answer:
Direct your vendor to the staff interpretations of 1005.17
1. Scope. i. Account-holding institutions. Section 1005.17(b) applies to ATM and one-time debit card transactions made with a debit card issued by or on behalf of the account-holding institution. Section 1005.17(b) does not apply to ATM and one-time debit card transactions made with a debit card issued by or through a third party unless the debit card is issued on behalf of the account-holding institution.
You did not issue the casino card and the casino did not issue the card on the institution's behalf. Therefore 1005.17(b) does not apply and you may charge a fee without obtaining an opt-in.