I have had a female hamster with fur loss and had a couple of threads about this at the time. I changed her diet everso slightly to the following:
3/4 oz of hamster mix, 1 small/medium floret of broccoli, 1 grape, 1 slice of carrot, small cube of apple, sprinkle of wheatgerm, 1 peice of tofu or peice of egg, 3 peices of dry kitten food,1 small (baby spoon) of baby food with 1 drop of oil mixed in (she has that as her starter).
The fur did grow back and when I initially took her to the vet she was treated for mites but it wasn't mites that caused the hairloss. Never did find out what it was but the diet definitely helped and she stayed on that mix for the remainder of her days.