Well, I've had a resolution to this problem for a number of days, just figured I'd update the thread.
All fuses were fine, as were cables and connectors. Checked and re-checked jumpers and wiring to safety equipment. Went as far as powering off the cabinet to do a cold restart and even after that the robot would not move. So I called it a day and decided that it would be best if I came back the next morning to get back at the problem.
Did just that and as a Hail Mary decided to poke at the buttons to make sure it was still locked up and wouldn't you know it the drives powered up.
Long story short - the problem appears to have resolved itself and the robot has been working fine since (so far ). I suspect a pretty stubborn version of a single channel fault (LEDs not lighting, the nature of the system integration of this cell itself, and a couple of other threads I perused lead me to believe this is the most likely scenario).
Thanks again for your help - wish I had a better solution for future folks troubleshooting their own issues.