First, the only thing we can be responsible for is our own actions, so no matter what she does, he is always responsible for his action if he strikes her. And that's never acceptable.
However, I do believe there are women who grew up in homes where they or their mothers were beaten by their fathers, and to them, that is what love and marriage is. They don't know any other way to related to a man.
All around us, people are dying in horrid tragic ways. There are car accidents and people falling down stairs and children falling into pools every day, and yet most of us manage to function. But if that person dying were our own loved one, we would be devastated. It is the love for the person that makes their suffering real to us.
Similarly, some women raised in these environments think at some level that if their husband didn't love them, he wouldn't get so angry at them, and therefore it proves his love. You sometimes see a related dynamic where a woman will flirt with another guy until her man gets furious. His jealousy is proof that he loves her.
Women with that sort of pattern in their minds actually seek out violent men. Because if she does her normal behavior (drinking, cheating, nagging, whatever) and her guy gets fed up, gets enraged, and maintains control of himself and goes out for a long walk to calm down or goes to a bar and gets drunk instead of slapping her, she isn't interested in him. She dumps him for the cretin who will hit her.
And then there are guys who like to play mind games and keep a woman unbalanced by criticizing her so that she believes he's her only hope at love, even while he's beating the crap out of her. He gets off on having her cowering at his feet, and normal women will walk off the first time he starts playing these games. But eventually he finds one with poor self esteem who buys into his verbal abuse, and they "fit" together.
It's a very complicated dynamic, and you can't blame just one party for the whole dynamic.
But when it comes right down to it, he shouldn't hit her. Period.