I used concealer religiously in a similar fashion, and during my research into it (while I never heard something truly conclusive) it was deemed pretty inconsequential to the growth of my grafts. I'd like to hear more on this, though, as I never got an absolute answer.
Slow healer correlation could be, but I've never heard of that; especially, in this case it's his scar that you are referring to and I was a very slow healer myself in that regard (my recipient healed remarkably well, though).
If I has to bet I would say that his styling is a main culprit here, and that he is hopefully just a slow-grower, as well.