What purpose is served by this editor's participation in Wikipedia? Does this person really qualify as a "Wikipedian"?
You can ask the same question of "social members" of tennis, bridge, or music clubs. Ultimately their benefit, if any, is indirect. Maybe they donate, maybe they encourage other users, maybe they resolve disputes, maybe they participate on mailing lists, maybe (as suggested) their user box edits are helping others.
No, I don't really think so either. But they're probably not more harmful than someone that makes some well-meaning but factually incorrect errors to a wide range of articles.
Steve