My male dog had this for a year. It was not allergies, not mites, not fly strike. He just turned two and in the last month, it has healed over. Basically he was missing fur on the tips and sides of his ears, and in its place would be dry, flay skin. His was not oozy or scabby and he never itched it. I use a dog bug repellent because we thought it was fly strike and he does get bit by little bugs in the summer, but then it came back worse over the winter (no bugs). His was not really that bad, so I just gave up after a while, and now it's healed. Maybe it will come back, who knows. I used to rub Dermalone ointment on it but it didn't seem to help. I read it can be "vasculitis" which I think is related to circulation. That would make sense in our case b/c my male has pretty big ears, lol.
Here's a few pics that show it: