If he's doing fine on the dry food, you shouldn't need to give him any
canned food. I don't give any of my dogs canned food, even the one
who has allergies.

Ditto that. And if you feel you want to treat your dog while he's on Z/D
(remember, it has to be exclusive), try baby carrots. Or take some of the
alotted dry kibble for the day and put it in a zipper baggie and pop it in
the freezer. The dogs love the cold crunchiness of this treat and you never
stray from the diet!