Deer seem to react different to brassicas in different areas. Some places they eat them to the ground, other places they won't touch them. If the local mill suggests them, they probably know that they'll work for you. You won't get great growth planted this late, but if fertilized well they should put on enough growth to feed the deer. Within 4 weeks mine were over 12" tall as reference. If you don't have some frosts before the rut, the deer may not be interested in them yet, but again that varies. I have no idea about bears.