Capture the dv footage. Load the DVD footage into the viewer. Find an easily recognized video frame or sound. Mark an in point or place a marker on it so you can find it again. Load the dv clip in the viewer and find the same exact frame. Note the timecode of this frame.
Load the DVD footage back into the viewer and go to the frame you marked. Use the Modify/timecode command to change the timecode to the timecode you noted from the dv version. Also give it the same reel name. Now the timecdes of both clips match. Take the DVD clip offline using the Make Offline command. You can elect to leave it on disk, in case something goes wrong. Connect your offline clip to the dv clip using the Reconnect media command. Your edits should now be correct and linked to the dv media instead of the DVD media. This sounds more complicated than it is…it’s actually quite easy and I have done it successfully many times