Gary:
I agree 100% with Bob (Iwire).
Although not REQUIRED by the NEC, I believe (as others) that a "quality install" would have a dedicated line to the disposal. Tapping the lighting off of the GD circuit more than likely will result in 'dimming' when the GD is started.
Without the nameplate data for the GD, I cannot give you a valid NEC Article to dispute the install, as you described it.
John
