...and if the cellular ones need cellular service for their GPS to work...
That's why I wrote my first post the way I did. GPS has nothing to do with cellular service. Some devices use a cellular location technique to augment GPS (for example, to provide rough location if you are inside where GPS doesn't work,) but GPS itself will never require anything but a GPS receiver.
Sorry about your mis-matched specs. Maybe you could get a bluetooth GPS receiver to make up the difference. Or maybe Apple would let you return it?