If you have had him for over a year, and he's had those since you got him, the hair won't ever grow back. It is also definitely not proud flesh. If you want to try something like MTG or Equus Mega Tek rebuilder you can, but I think it would be a waste of money. I would just leave them alone, and look at is this way. It adds character. I had a mare with nasty scars all over her back legs, and a bit on her front, and it was a great topic of conversation, as we would speculate what she had done to herself, as I didn't know, and was told several different things.