Weedon saves White Fang, which may make him the hero in some ways. But more importantly, he teaches White Fang to put aside all his hate. Guides and mentors usually show up early in the story. Weedon shows up later, but it doesn't change the good things he teaches White Fang. He's like the big hug at the end of the finish line: the one to show him that life isn't just pointy and bite-y and cruel. That puts him firmly in guide-mentor territory… late arrival and all.