I believe intent is important when discussing the possibility of forgiveness and rehabilitation. Moash has thought this through. He chose to suppress his emotions to allow him to commit acts of pure malice. When he was confronted with the reality of his actions, his first instinct was to run back to Odium. He knows what he is doing is wrong, and does not want to change. This would make it more difficult to trust him even if he does ask for forgiveness later.
Dalinar on the other hand, was horrified when confronted with the reality of his crimes. He could have gone back to the Thrill to cover his pain and guilt, but chose not to. He knows what he did was wrong, and wants to change. That is the difference for me.