Psychologically speaking, Is it possible for the abuser to be traumatized by what he did to his victim?

That's a very good question. I don't have the answer, but one story a friend shared with me about what happened to her seemed to imply that her abuser was horrified, at least for a moment, by what he just did.

Any abuser however who is also a psychopath or just plain sadistic would I think be much less likely to be traumatized. Psychopaths tend to feel little or no guilt about what they do. Sadists take pleasure in giving others pain, so again, probably not so much guilt.

I think the best candidates are probably the people who thought they were pretty normal and decent, but who ended up doing something terrible to someone else. They'll more clearly see the mismatch between who they thought they were and what they did, and so be traumatized. I think also perhaps a person who acts as part of a group, such as a soldier, and then has time to reflect on their actions when alone (such as when they're back from war) would also be a good candidate for what you're describing.

Yes, those images don't go away on their own. The stress that led them to abuse leads to more abuse that leads to more stress, so if they keep it up it eventually overwhelms them. If the abuser stops abusing they regret their actions and have to find ways to resolve their regret.

guilty conscience?

yes

Yesss.

possibly