0-10V circuit in DRd with D20

It's likely they are using the 0-10V card inside the DRD rack for the dimming control.  

If the power supply/ballast is being powered by the D20 that's another story.

If you 0-10V light is on, and you physically breaker off the D20 does the light go off in the space? 
There's always a chance they landed the old circuit from the DRd rack into some panel board?

And yes a CC20 or R20 would be recommended, R20 being preferred.  Does a D20 work, sure for a bit, but you are still going through the choke of the dimmer and the driver is getting a clipped power signal, which overtime (basically a little mini electrical hammer hitting the electronics inside the driver) is going to cause issues to the 3rd party driver/ballast.  Could last 2 hours, 2 day, 20 years, you never know.

It's likely they are using the 0-10V card inside the DRD rack for the dimming control.  

If the power supply/ballast is being powered by the D20 that's another story.

If you 0-10V light is on, and you physically breaker off the D20 does the light go off in the space? 
There's always a chance they landed the old circuit from the DRd rack into some panel board?

And yes a CC20 or R20 would be recommended, R20 being preferred.  Does a D20 work, sure for a bit, but you are still going through the choke of the dimmer and the driver is getting a clipped power signal, which overtime (basically a little mini electrical hammer hitting the electronics inside the driver) is going to cause issues to the 3rd party driver/ballast.  Could last 2 hours, 2 day, 20 years, you never know.

This is exactly what I was thinking.  Thanks for the input.  I'll see what details I can confirm.