MP, your whiltelightning will work on sctratches too.... You just have to tie the bag higher on the leg to cover the scratches or mud fever.
It may bleach the hair a bit lighter, but a small price to pay.
scratches are an indication the horse is trying to expel some "Crap" in its system, I have seen horses go through a multitude of skin issues while transitioning to BF, including warts, (@ 4 years old) flakey skin, scratches etc, all at once for a good month, then POOF, in great shape. Really bizarre.