I can't answer your question but I have been looking into the wii netflix service, sounds interesting. Haven't set anything up yet but I'm probably going to do it in the next week or 2.
The only thing that I do know for sure is that you can have up to 6 different devices associated with your account at 1 time. Not yet sure if you can use them at the same time though... it seems like you should be able to.
http://www.nintendo.com/consumer/systems/wii/en_na/netflix/faq.jsp
