Since Gitmo and other terrorist spa / resorts are not 'public' areas, I don't believe that the issue of royalties would apply because the 'music' is not being publicly broadcast.
The usage in this case could be likened to playing music at a party for your friends, with the notable exception being that the terrorists are most definitely not friends of the troops and my understanding is that the food served to the terrorists is considerably better than what's served to our troops and quite a bit better than what's been served at many parties I've been to. The terrorists are also not allowed to leave the party at a whim although that is a matter that the Left / terrorist enablers are desperately trying to change.
Thank you! that was very informative.