A minor scratch may or may not be written up -- I think if it is not major then likely overlooked. Especially on a bumper.

if it IS written up, the first thing they'll check is if you have LDW. If its a minor repair and you have LDW then they may just go ahead and repair and you'll not think of it again. If they repair it and look into your eligibility for the LDW they may or may not be able to tell, and therefore you may or may not hear about it again.

I rented a car from National using a certain corporate discount I found on FT that included LDW that I was technically not eligible to use. While I had the car, someone clipped the passenger side mirror and broke it off completely. When I returned the car, it was noted by the agent. She looked and commented that I had LDW at the return and said because of this "don't worry, we'll fix this and you are clear." Hopefully your experience will be similar.