I find the store bought oatmeal shampoo really doesnt do much.. but if you take tea tree oil in water with oatmeal (grinned to a bit of a powder like) mixed enough to a paste and put in a sock (that you'll end up just using for this) and then rub it on the areas that is effected helps better then the oatmeal shampoo itself. I have found the anti dandruff (its also allergy friendly and lowers the allergies on the fur) helps with any scabs or flaking from the allergies themselves.
If you take a bit of lavender (has to be the safe essential oil), tea tree oil, vitamin e, and water use as a spray on the spots help too. I double my vitamin e in it sometimes.
my issue now is just getting our westie mix, Scruffy's fur to grow back in the few spots about the size of a fifty cent piece to grow back and around his collar line (which he really doesn't wear one unless we go some where) as it is kind of thin there still.