Cat allergic to nickel?

Has anyone ever heard of a cat being allergic to nickel - the metal that's in fake jewelry and metal ID tags? I just noticed that one of my fosters has a fairly big bald spot with a couple of small wounds/scratches in it. It's right below his neck where the ID tag hangs so I suspect that's what's causing it. He's also taken his collar off 2-3 times in the past week or so and I couldn't figure out why. Now I'm wondering if it's because of the tag bothering him. I'm allergic to nickel and the little wounds kind of look like the wounds I get if I wear something with nickel close to my skin for too long.
If it's the tag that caused it I'll just get him a plastic tag, no biggie, but if it's not I'm worried. Does anyone else have a cat with nickel allergy? If so, does it cause these symptoms?

Yes, it is not uncommon. My Bonaparte has a sensitivity to all metals and gets terrible eczema on his neck and chest if I use a metal ID tag or a collar with metal studs. It takes several weeks to clear up, even using topical and oral anti-histamine prescribed by the vet.