If she has no intention of leaving him you need to be careful how you say it to her. Some times people in these relationships will fall out with the person who is trying to help. I knew a girl once who was in an abusive relationship her mother and sister tried to talk to her about it but she fell out with them not him.

Its hard place for you to be in right now i understand that and i dont envy you at all. If you are going to tell her this info you found out about past exs my only advice is say it once and once only. she get annoyed with you if she feels like your saying it to often and it could be something that she herself doesnt want to confront. Say it once and when or if she does decide to leave him or when she needs a shoulder to cry on be there for her.

Advice often makes people angry even if its something you need to here. She could end up avoiding you and you could lose a friendship which would suit an abusive partner he'd be delighted no doubt. I wish you luck whatever you decide to do