I don't know how DVC plays into it...but you can only use DD on the ship to settle your shipboard account. It cannot be used at any of the bars or shops onboard. No cash in fact can be used except to tip the room service people. All transactions are put on our KTTW card. You can either assign a credit card to your KTTW card or pay it off with cash, DD, travelers checks, etc. as you go. This has to be done at Guest Services.
MJ