So, OK, ACTUAL CULLEN DISCUSSION time. Cullen's lip scar. We know from Brianne that it was just an artsy addition from the artists, and she imagines he got it Kirkwall. My question is: how do you get a scar like that?? If you're fighting someone and their sword hits your face, would it really only score your upper lip like that?? Or does it have to be a shaving scar or something equally inane? Or did he get a split lip from a fist fight, and it just didn't heal right?
I think you're imagining battles as more... organized than they really are. Oftentimes it's really just people going at it willy-nilly and bashing each other. So it could be anything, really. Perhaps his face ended up jammed against an enemy pauldron, or his own shield was shoved into his face, or (as you suggest) a split lip from being punched in the face. Weapons flying around, bodies flying around, spells flying around -- it can be quite chaotic. Or maybe he got it during training, or just some fluke accident?
Bonus points for any fic writer that makes it something boring or silly. 
My Inquisitor has the scar option with the upper/lower lip, in addition to the crescent over the right eye socket. I have a non-glorious head-canon for the eye scar, but nothing for the lip one, which I never bothered to come up with.