I would say it is, not animal cruelty as in the kind of sick bastard who beats up dogs and stabs cats but more along the lines of 'just plain retarded'. If you could find a tattoo artist who was dumb enough to tattoo a dog or put earrings in a cat then I'd eat my hat, also the practicality of doing that would be pretty damn impressive and yet also cruel since you'd be pinning down your pet so someone can stick needles and ink in their skin.

No

Animals can't give consent, and don't care about their physical appearance like humans do. To them, it's just uncalled for pain. If you want a cool, personalized graphic that everyone can marvel at, don't be a coward and have another creature face the pain for you.