You can bathe your ferrets, so long as you don't do it too often. Once a month is the most frequent I've ever heard a vet or other relatively expert opinion on ferrets express.
Be sure to use shampoo formulated specifically for ferrets, as they will be less harsh on their skin and the oils they naturally produce.
The few times I bathed my ferrets, I used this product, and had good success with it.
Aside from infrequent bathing, you can help cut down on the musky smell associated with even descented ferrets by cleaning their bedding and any other washable "furniture" they might spend a lot of time in (tubes, hammocks, etc.) frequently. Bedding in particular tends to pick up a lot of the oils, and it becomes a feedback loop of stink if you don't keep them clean :)
I found this article that provides some good general tips on bathing your ferrets that may be helpful.