Backdriving PG71?

[scuba1000]

We are planning on using a PG71 gearmotor to rotate a pneumatic cylinder on our bot for climbing. Currently the design calls for the motor to be backdriven (I think that's the right term) to follow whatever angle the cylinder ends up at. It is not connected directly, but uses a lead screw.

Sorry if the setup explanation doesn't make sense, but here are my questions:

1) Considering the high-torque gearmotor and the leadscrew and nut (kinda similar to a worm gear i guess), will the motor even reverse when a large force is applied to the nut. We can't really test this right now because it involves connecting the leadscrew to the shaft and we don't have any coupling to do that, and I don't want to turn down the shaft of the leadscrew just to test it.

2) If the motor is backdriven at relatively slow speeds, will it hurt a Talon or Jaguar? I've pushed the whole robot when it was on and nothing seemed to happen, but my mentors are weary of this. I was thinking of adding a spike relay upstream from the talon and switching it off when the motor is finished rotating. That would solve the problem right?

Thanks