Definitely not absolved of his war crimes, but Return of the Jedi did give him a clarity of mind before he passed,
Luke: Because there is good in him, I've felt it. He won't turn me over to the Emperor. I can save him; I can turn him back to the good side. I have to try.
...
Luke: No, you're coming with me. I won't leave you here. I've got to save you.
Anakin: You already have, Luke. You were right. You were right about me. Tell your sister... you were right.
If they choose to have Anakin as a Force ghost appearing to Ben, I'd expect some kind of "It's not too late for you" type dialogue. Honestly the only thing that bugs me if they do it is Ben has hero-worshiped Vader, not Anakin, for how long? If all he needs to hear is Anakin in death being on the Light side and not the Dark, why wouldn't Anakin have appeared to him sooner?
If Palpatine just shows Anakin as a Sith illusion or something to rattle Ben on being unable to live up to his familial talent though, that'd probably be fine.