Well, SDV is used in conjunction with your cableCARD device, be it third party or be it the cableco stuff.
SDV is well outside the Replay loop. The Replay may give the signal to the cable box to change channels, but that's all it knows. It's up to the cable box to send the signal down the line to actually get the channel delivered, and it does it via the SDV box(es).
The only issue I can imagine is the delay between Replay sending the channel change request and the whole cable box/SDV thing actually delivering a signal. Will Replay go ahead and record those few seconds or whatever of "dead air" while the cableco is sorting all that out?