I know one illustrator, and one graphics designer (English and Turkish-Candian respectively). I know one of them has a very successful career. I'm not so sure about the other one, as I didn't know him for that long, but he did have a job within a Japanese firm. The illustrator is freelance, and always has been. It's definitely possible, but I think being in Japan will help your chances of this for many reasons - one is that it will expose you to the style that Japanese design houses are looking for. Speaking Japanese, of course, won't hurt.