It only cheapens veagnism by grasping for any famous name to add to the roster of people to say "So-and-so is vegan, so you should be, too!"
Sometimes people will ask me what celebrities are vegan, and the only ones I will always say are 100% are Emily Deschanel and Joaquin Phoenix (oh, and Geezer Butler), because they're both long-term vegans and activists. Sometimes I will say Weird Al is 'almost vegan'. So many people announce their veganism, do work for Farm Sanctuary, then a year later they're on Jimmy Kimmel talking about bacon wrapped meatloaf or tweeting about how they had egg whites for breakfast (ahem, Ginnifer Goodwin and Bob Harper).
And yes it exciting when Ozzy and other people say they watched Forks Over Knives and changed their diet, but no-fat 'plant-based' eating is just the latest fad diet, and after the next new thing comes along, a lot of those people will follow that. But by publicly announcing these things, they're bound to influence readers to investigate veganism, and if even a few of them stick with it, there are more vegans in the world. Yay!
I'm not a fan of violent sex offenders and obviously I don't follow Mike Tyson around, but i'd like to think that people can change and be rehabilitated.