[Steven Smith]

One of the suppliers might be able to chime in a little more definitively, but I would not anticipate vibration or g-forces associated with a moving arm to be excessive for the motor controller. You already experience quite a bit of this on a moving robot that slams into walls, other robots, defenses, etc.

As alluded to earlier, what I would be concerned about is wiring. The controller should be firmly affixed to whatever solid item makes up your arm, and your wiring should be strain relieved to that surface as well. You need to be aware of your connectors and their vibration resistance, screw terminals need to be torque'd to spec, etc.

If you have a section of wire that will be in repetitive movement, it needs to be of a high quality wire intended for repetitive movement (typically very high strand count with a more flexible jacket). If you imagine wiggling a paperclip back and forth until it breaks, the same concept applies to wire in a moving joint. Watch minimum radius bends (aka, don't lock down either side of the wire, forcing all the movement in a 1/4" area, but also can't leave too much wire flopping around such that it can catch on something that binds.

TL;DR - Probably not best practice for most folks, but not because the motor controllers can't take the movement, because you need to be really careful on the wiring side.