[Al Skierkiewicz]

Dave,
The mass balance is a technique where mass is added to the mechanism that is vibrating and then the mechanism is isolated from the source through very flexible material. This is a technique that has been long used for acoustic isolation for things like turntables up to entire rooms. Radio, TV and Film studio design regularly will isolate the floor with springs and dampers and then build the entire studio on the floating floor. Mason Industries makes some pretty good isolation and has interesting discussions on their website.
You can try using some really spongy material to hold the camera and mount on the robot and that might quell some of the vibration. Be advised that the 3/4 throttle vibration you observed could be the sum of several different vibrational sources that all contribute at the frequency. Is it possible to isolate the wheel and motor assembly from the rest of the robot using rubber isolation?