What are you feeding? If there are a lot of grains in the food it could be causing some dry skin. The Yorkie Splash and Shine products are some of the best products you can use right now as far as grooming. Because they are all natural it does not have the detergents in it that most regular shampoos use so it won't strip the skin of it's natural oils.
I would take a close look at what you are feeding. There is a very good supplement you could try. It has a very digestible omega 3 in it as well as enzymes and other things that are cooked out of kibble.
The Missing Link Canine Formula Super Food Original Supplement at PETCO
I would make sure he is doing well in his recovery before starting anything new.