wet cat food can be a good source of extra protein when needed...however I've moved it to the medical need category.
Adding meat protein to your chickens diet is important...as I recall you freerange your chickens so they get that on their own when they eat bugs and frogs and such. But every once in a while you'll get a chicken that gets anemic or maybe it's going through what we call a hard molt (that's when they lose almost all their feathers at once).
Cat food has the meat proteins, but it also has a lot of other fillers and such. That's why I only use it if I really need to.
edited to add: a good source of meat protein is your own leftover meat---they don't mind the grissle either! If you're a fisherman or hunter...you can also give them the meat that you don't eat...my chickens surround DH and I when we're cleaning fish, or deer....they just love it.