I don't know anything about halter, so I can't elaborate further on anything that's been said here about whether or not it effects placings, however, whether it did or not, if it were my horse I'd probably try to conceal it just to improve appearance.
Of course, I'm the sort of person who braids manes and polishes hooves for a schooling show.
Amber has collected a couple of small dings on her, mostly just roughhousing with her mares out in the field being silly. I'll probably still try to put something over them when we show.
Cinnamon Whiskey 11 y/o 15hh Chestnut AQHA mare, 2'6 Jumpers