If they can make it look good, sure. But if it might have bugs (clashing wit head gear) then it's not worth it really.
That wouldn't happen, unless it was an outrageously big scar. But there is absolutely no reason to fool around with meshes when you create basic scars. What they have to do is use graphic artist magic (this is a really, really simple thing to do for at least the gunshot) and put a bullet scar on your head. Make a custom race specific to the Courier, and bam, you've got a gunshot. I have it on my character. But yeah, scars would be nice, but I think there is an issue with them not wanting to force them on the player. It's a tad more silly not to make a subtle gunshot wound no matter what, but what can you do? Also, who says whatever experiments will happen to you are going to produce scars like Christine? They are probably entirely different.