Dev (#6) - MotionPlus and Nunchuck (#135) - Message List
Just to note that the archery game in Wii Sports Resort is definitely using the MotionPlus and Nunchuck at the same time, so it is possible.
The main controller is held vertically, which causes a singularity in the roll you would get from just the accelerometer reading; it must be using the gyro to determine delta-roll. This is used to aim the bow left and right. It can't be using the IR for aiming because the camera's pointing straight up and can't see the TV.
The acceleration on the Nunchuck is simultaneously read, it's used to detect pulling back on the arrow.