Reports are coming in that Vader will be exclusive to the PS3 version and Yoda will make an appearance on the 360 only.
If they ever decide to make a Wii version, my guess that good old Obi-Wan Kenobi or Luke Skywalker would fit the bill. Think about it:
Vader: Black like the PS3
Yoda: Green, a color associated with the Xbox brand
Obi-Wan/Luke: Blue lightsabers, the secondary color for Wii.