Odd...I have two thoughts but they don't cost much to try.
You might try Braggs Organic Vinegar
Apple Cider Vinegar for Dogs by Alicia McWatters Pet Care
or you might try Bag Balm which was created to heal cow udders that were all cracked etc. You can pick it up at Walgreen's...I use it for my chapped lips and have used it on the dogs many times..
Bag Balm - Wikipedia, the free encyclopedia
What does the vet say?