I've been designing a "dual motor" system to try to compensate the vibration acted on the adapter. In theory, it would work. However, I still can't get it work. Heavier GG will cause more vibration force. It might shake the camera.
So it is neccessary to eliminate the vibration.
Here is my design. The design consist of 2 vibrating motor parallel connected to the same power supply. So that the motor spin in similar speed. And the offset weight of the motor is connected by a thin and small carbon rod. To ensure they spin at the same speed. And 2 offset weight must spin in the same direction, and 180' "out of phase". So that at any given moment. The offset force produced by them are exactly opposite.
As a result, the force acted to the camera by the GG holder assembly should be cancelled by the "compensation motor". In perfectly ideal situation, the camera and the adapter case, 35mm lens, should receive 0% vibrating force. While the GG assembly is not affected.
But however, after my first test. Both motor vibrating in the same speed same direction 180' out of phase. The "tube" of 35mm lens still vibrate like before.
Here is a drawing of my design.

My first thought would be that you have created a moment arm about the center of the carbon rod connecting the two weights 180 degrees out of phase. As a guess, I'd expect the assembly to oscillate about that point.

You could achieve this with a single motor fixed to the adaptor and a bearing pair, shaft and eccentric weight at the groundglass carrier, a better solution in that the resistive mass of the second motor and fragile feed wiring would be eliminated.

However the limited small-run cost-friendly availability of miniature bearings and shafts means the use of the second motor is probably the most cost-effective way of doing it, even if you do not provide power to it and guts it out to reduce resistive mass.

If powering the second motor, I would be inclined to add control over the power to this motor. Fairly simple coarse controls over the power to one of the two motors would translate to smaller increments to vibration rate and if feed wires or one motor fails, the device will continue to operate. Applying varying power to a second of two mechanically linked motors was a common method of smooth control of transport and drum speeds in older videorecorders.