Its actually not trademarked - the only trademark on file for Wii is an expired one from an old company.
Apparently nintendo have submitted a trademark application however those take time.
In addition, Nintendo have a history of being fine with domains featuring their console titles provided the sites do not contain anything negative about the product, and the owners do not claim any official relation with the company.
My opinion on the domain - pretty nice catch, not one of the best but still a decent one, i'd probably say low-mid XXX, as wiichat.com would probably be prefered to this domain.