It has been known that WiiWare developers can take advantage of features on the Wii such as the weather channel, Wi-Fi components, and even the Wii message board. What hasn’t been elucidated, however, is whether those who wish to put their games up on the Wii Shop Channel would be able to use Miis in their games. In an interview, Tom Prata explains that developers “are able to discuss with Nintendo about the use of the Miis.”
I assume that, depending on the type of game, Mii characters would be able to be integrated. Specifically, Nintendo would most likely not allow developers to put Miis in their game if the title contains mature content.