As far as we know right now, Wii and Wii U's relation seems like a one-way street. Wii U can see into the Wii and change things (settings, updates, etc.), but Wii can't see out (except to tell Wii U it's quitting when the user goes back to Wii U menu). This may change though, once it is explored more.
For settings, many seem to think the Wii U menu just updates SYSCONF (the file where settings for a Wii are stored) when we change the settings on Wii U. That also would make the most sense, since any Wii code that checks that file for settings is going to expect it to exist and be accurate. We won't know for sure though until we can dump and examine it.