We lost our sweet Polly, our camping companion (dog), last Christmas. Gnocchi, our new kitty came to us that October, and has taken over the camping companion status from Polly. I never noticed ...
IMO: The pet fee is in place to pay for any damage/mess from pets, and to pay for those dog waste bags that the campgrounds provide. Also, it goes toward maintaining a fenced dog run,(if the CG has one). An inside cat would not be applicable.