Dunno if they have or not, but thats mostly because the engines are so specialized that they're only good for the game they're using it in.
One example is porting and updating the Zelda 64 engine (which is a heavily modified Mario 64 engine) to the GC for Dinosaur Planet. That was still technically within nintendo, but to a second party from first.
If the engine is good enough, I really don't see why they couldn't license it. It would mean more great games on Wii, especially shooters, which is practically what they designed the thing for.
Witty signature here...
Wii: 14 million by January I sold myself short
360: 13 million by January I sold microsoft short, but not as bad as Nintendo.
PS3: 6 million by January. If it approaches 8 mil i'll eat crow Mnn Crow is yummy.
With these results, I've determined that I suck at long term predictions, and will not long term predict anything ever again. Thus spaketh Crono.
