That is a good question. In "The Vampire Genevieve", in the first chapter or so, she talks about how slowly her wounds will heal due to the attackers using silver weapons (if I remember correctly). Now I think she also says that she lost a hand a couple of hundred years ago and it took her quite a long time to grow a new one. So if that book is considered cannon (which I highly doubt) I'd say that your vampire's skin will come out smooth eventually. Besides most vampires have access to magic, so it wouldn't surprise me if they just remoulded their faces should they be badly damaged.
Personally though, I'd let him keep his scar just because it looks cool with a huge gash running over your face (unless the guy with the scar is is you yourself...).
Now if you'll excuse me I'll have to dust of Genevieve and start reading it again.