Very interesting.
One point I'd like to make: The Roland V-Bass doesn't translate your playing to MIDI notes. It does advanced polyphonic signal processing - sort of like one POD for each string. The V-Bass can't trigger sounds from another MIDI device.
Things like the Axon or the Roland GR-20 does translate your playing to MIDI, and can thus control another synth.
I don't know much about uprights and V-Bass though. I 've read in the owners manual that the V-Bass has settings for things like scale length (and other settings to describe the physical instrument you're playing) and that the scale length can be 914mm (36") at the most. I don't know how this would affect the working of the unit, if the scale length of your upright is 41" or something.
Perhaps you'd like to visit
http://www.vbass.thedrillgun.com/ and ask the guys that actually have a V-Bass. I don't have one, I just wish I did.