Since a single Wii can only have four Wii Remotes and four GameCube Controllers connected at the same time, a combination of the two is needed for 5 player games.
Since a single Wii can only have four Wii Remotes and four GameCube Controllers connected at the same time and while the Z button on the GameCube controlers are held during start-up. A combination of the two is needed for 5 player games.