Since it's a hat-like feature, I figured it would probably work with Pet Mirrored pets that can also wear Pepe on their heads. And, ta-da! After testing, it turns out that most Pet Mirrored pets that can wear Pepe will also wear the Fruit Hat. The Cogblade Raptor sort of wears it, but not quite. It sinks too far into the pet model's head for it to be properly worn.
Here are some screenshots of a few Pet Mirrored pets + Pepe + Fruit Hat. To wear all three you need to use Pepe and the hat first, before using the Magic Pet Mirror.
(click for larger images)
I've tried using the Fruit Hat with other pets, but so far the rest refuse to wear it. I guess only those tolerant enough to put up with a little bird are willing to also put up with a fruit bowl lol.
One silver lining for pets that don't want to cooperate with stuff on their heads -- if the Pet Mirrored pet has a dance animation (Brightpaw and Unborn Val'kyr for example), the Fruit Hat will put you in a constant state of dancing haha.
I've updated my list of Pet Mirrored pet animations to note which pets can wear the Fruit Hat. Just CTRL+F (or whatever the search function is on your browser) to search for "Pepe" and it should highlight the results.
It's a shame that more pets can't have Pepe + hat! :P