That's already covered for this action.
Remember, checks are a flag (in the coding sense). It is either set, or not. You've already earned a Cruel check this winter phase, so you can be a murder hobo all campaign season without incurring other checks on cruel.
Vengeful looks different. That's hunting down every Saxon in the land to murder them, their families and their horses - that sort of thing. Leaving Arne lying on the beach to go murder Saxons is more of a Vengeful act. Vengeful is disabling someone, then making him watch while you do more things to hurt him, and that kind of thing.
