I wore a headband with ears on it in a US high school for a little over half a school year (from late November until graduation). They (at least used to) sell freaking kitty ears at Hot Topic. Ears are, far as I'm concerned, perfectly acceptable accessories, especially if they're mounted in a way that make them functional (eg. a headband, hair clips, or other accessory to keep long hair in check). I would totally think something like an animal-themed hoodie with ears on the hood would/should be acceptable, as well.
The only two people who gave me grief about the ears was one girl who already had it in for me for ridiculous unrelated reasons (short story: she was an airheaded bully), and the mother of one friend-of-my-brother's who basically "forbade" me from wearing them in public when out with her son and my brother. I've no clue what her deal was.
I'll also note that for some dumb reason (like, I literally don't know why it turned out that way) I didn't really have any other hair things with me at the time, so when said mother objected I just ended up wearing my headband upside down so the ears were on the back of my neck, under my hair, whenever I knew she might see us.
BUT I'm also very far from the fashion police. I basically think people should have the right to wear whatever they're comfortable in, in public, so long as it's not blatantly offensive/excessively revealing in inappropriate venues.