Disney Gift Cards are not accepted anywhere on Shades of Green (even though SoG is on-property, it is owned by the U.S. Department of Defense and is not considered "Disney property", as GCs go).
I would imagine the same rule applies over at the Bonnet Creek resort (since that resort is largely not considered to be a part of WDW and is owned/operated by Wyndham).
Perhaps the same rule applies for the 7 non-Disney hotels/resorts situated near Downtown Disney?
GCs are also not acceptable for payment for gas/food items/snacks at the three Hess Express gas stations/c-stores on-property (as those facilities are all operated by the Hess Corporation).