I assume they do. The Boss Book says that they made the compact pedal version because the rack effect was such a success. Mounting BBDs for 2 channels into a 2 unit rack module was easy but getting everything into a compact pedal was much more of a challenge but by using two layer PCBs that managed to squeeze it all in.
It's probably not identical to the SDD-320 but I suspect they share a lot of circuitry.
They are very similar sounding units. They're harder to find than any of the compact pedals unfortunately. I've been looking for one for years and have only run across one that was way over priced.
I've never actually heard the rack unit. I have the same experience as Boss Freak - whenever I find one of these units they're so overpriced that I just keep walking.
Amazing to see that Boss did achieve to get the sound similar to that of the rack unit for such a small pedal as the DC-2 and 3.
The micro rackunits may tell us a similar story. Looked at a reverb yesterday and it does have similar reverbs as the ones which can be found on the RV-2, 3 and 5.
In case the compactpedals do sound very close to the microrack units, the only reason for gettting a micro rack would be the greater flexability of connections, which could serve as and advantage for recording and mastering.