on many of the dogs I groom. I have never seen the hair come back normally. It is usually from the rabies shot, and it just happens to some dogs who have sensitive skin.
Sometimes the hair stays gone and sometimes it comes back in coarser or a different color than the original fur. It if from the cellular structure changing due to the damage of the epidermis from the shot.
I have never seen it fill in with normal fur to match the rest of the body, but I think anything is possible...
Sue & Cricket