Well, yeah.. higher power will last longer at the same voltage.. rechargable = 1.2v normal disposable jobbies = 1.5v (which is the correct voltage for the wiimotes)
I'm not sure how it compares between 1.5v (say 1800mHa) and 1.2v (say 2400mHa) becasue the later extra 600mHa will theoretically be used up for the missing 0.3v between them... (I think that's how it works....?) Works in my head though (not batteries, that is! lol) and for a quick explanation.
But, yea.. higher power = longer.
And, don't take it as gospel, but I can't see there being a problem with rechargables (but I'm not a technician, and I'm no master of the wiimote either!)