CMs most likely won't touch the joystick on your device. If it makes you feel better, you could put a clear shower cap over it (that's what I use for rainy days) or an old sock, I suppose.
*If* a CM has to move your personal mobility device, they will likely find the red lock/unlock levers (on power chairs) or the brakes (on ECVs) and they will usually push the device out of the way. By simply applying more pressure when pushing to one side or the other, they can "steer" without touching the controls.
Generally speaking, you will see CMs moving around strollers way more than anything else. Just ask any CM in the area where you can park so that your device won't need to be moved, and it should be just fine.