I received an answer from Disney itself regarding gift cards...
The Disney Gift Card can be used as payment for a
Disney Cruise Line
vacation through Reservations or online at
www.disneycruise.com.
If you would like to use your Disney Gift Card to settle your onboard
account, indicate 'Cash' as the form of payment on the Payment
Authorization Form online. Once on the ship, take the Disney Gift Card
to the Guest Services Desk on Deck 3, Midship and the payment will be
applied to your shipboard account.
The Disney Gift Card can also be purchased, redeemed, or reloaded
onboard the ship. In addition, Guests who purchase a Disney Gift Card
onboard will be able to choose the exclusive Captain Mickey and Minnie
themed gift card.However, the Disney Gift Card cannot be purchased nor can additional
funds be added to the card at the
Disney Cruise Line terminal in Port
Canaveral.
The Disney Gift Card is valid for purchases until all remaining funds
have been depleted from the card. Please keep the Disney Gift Card until
after travel has been completed in the event a refund is necessary.
To purchase a Disney Gift Card, please go to
www.disneyshopping.com and
type 'gift card' in the keyword search box.