When Hermione's cursed by Dolohov it triggers... something. Something primitive and magical, like Draco's heritage. Draco Malfoy isn't as heartless as everybody thinks he is. Just because Draco's a Veela and Hermione happens to be his mate doesn't make him 'good'. Hermione's not all good either, but she's not like Draco. They have each other, and Theodore Nott and Luna Lovegood.