There are no McDonalds in the parks, per se. There are restaurants that serve certain McDonalds products (namely fries and chicken mcnuggets) like Restrauntausaurus in the AK. There, if you order a burger/fries combo you get a WDW burger and MK fries. These are run by Disney, so no, you couldn't use McDonald's GC there.
HOWEVER, there *IS* a bona fide McD's in DTD, and I would assume that they would take McD's GC.
Good luck!
N.E.D.