I don't believe arm control with a Wiimote would be stable at all. I played Wii Sports at a party a few weeks ago, and I was always crooked or off or shaky. Combine it with jumping up and down when you succeed at something and BAM you just hit the ref in the head. It would definitely take alot of practice and discipline to pull off.
For driver control, well, I played Descent 1/2/3 and could fly off of 3 axes at once using a single joystick -- it was sick and nothing but fun. All of those wierd hellical patterns you get from a spherical coordinate system? Yea I could fly those. I guess I'm a little biased there, but I will be stubborn and say that a single joystick is the best way to drive a robot.
On the other hand, with a hard-mounted WiiMote on your robot, you could get some serious sensor feedback control if the RC/OI would ever support it. I've already posted that idea
here for future games.