Chinchillas would most likley not hurt a chick on purpose but they are fast and do like to "spring" off of things so a little chick may get hurt. Kiln dried Pine shavings and aspen are perfectly safe for chins. The other thing I would worry about are illness, Coccidia and Salmonella both come to my mind right away and with both being such fragile creatures I wouldnt chance it. Also while chicks may be ok eating chinchilla food (wouldnt recommend it) chinchillas could get very sick if hey attempted eating even a bit of chick food with their sensitive digestive sysem. Also kind yucky to think about but chins being semi-low to the ground, if a chick pooped on one it wouldnt be easy to clean out of chinchilla fur since its so dense and soft, water baths may not be an option if conditions arent right and it coud end up in a big fungus-y mess!