I've heard and read that manually jogging a CNC machine (e.g. with a jog knob) could potentially induce a back current into the motor controller, causing damage. Is this something to be concerned about when using the BlackBox controller and the Nema 23 motors from OpenBuilds?
Correct, you never want to use mechanical force to spin the motors as they then become generators pushing voltage back into the stepper drivers. This applies to all stepper motor systems.