Even if the product is 100% aspen, an animal can still be allergic to it. There's no natural "hypoallergenic" material that is guarenteed to never have anyone/anything have a reaction. You can be allergic to anything, so you should always be cautious with any product that you haven't used with your pet.

I'm glad the hedgehog will be okay. I had one of my dogs react to cedar when I stuffed a dog bed with cedar shavings thinking that cedar was good for dogs. Not for THAT dog, although she'd never shown an allergy before, nor did any of the other dogs react to it. You just never know.