I'm sorry you're so aggrevated! I don't blame you at all! I was also abused as a child and I don't condone hitting a child at all.
If I were you, I'd just sit S down and tell him that his attitude lately is unacceptable and he's old enough to understand that and how to try to defuse his temper, anger, etc. I would also explain that H isn't all straight in the head right now and ask him to please blow off the smacks his father choice as discipline. I only say that so he doesn't feel as small as a mouse from getting smacked in the head like that.
