I would think anything you can bill back to the room, would be eligible to pay off with a room credit. Could be your resort fees, dining, parking, etc. The bill will total all that you owe, subtract your credit, then you pay the rest.
Back when I worked in hotels, we sometimes offered categorical credits as service recovery gestures. So, if the problem was related to food & beverage, the credit was limited to food & beverage. This was done so that the department that caused the problem ended up absorbing the cost of fixing the problem.
Other times, we'd offer a general credit that was good for almost anything at the hotel. Those open-ended credits were for service recovery from non revenue generating departments (like Housekeeping).
To make things more confusing, some hotel restaurants, retail stores, and spa facilities are operated by third party companies. In that scenario, a credit issued by the hotel might not be valid at those locations.
Here is the contact page for the Walt Disney World Swan and Dolphin hotels. If for some reason you don't want to call, click "General Comments" and use the web form to send a message.
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