Dave the thing that's concerning me is that Analog Gnd is shared with the Common Gnd to the outputs and not isolated. I'm sure it will work as I described but it's not a good setup in my eyes for the reasons Doddy stated with noise etc feeding back into the Analog and vise versa.!

Personaly I would feel more safe by using the outputs to control a relay and then feed the For/Rev thru it's contacts then if any stray voltages/currents get fired out they don't fry the VFD logic. You still may get noise issues and the Odd strange behavior but at least the VFD is safe.

Also regards your earlier comment about twisted wires and not being too concerned about noise, then if your actually wiring the machine rather than just testing on the bench I strongly suggest you re-think that because if you get any noise issues it will send you crazy and I mean proper hair pulling sessions so it's worth doing correctly straight off the bat.