We have a large Exchange site and snap mirror the database over the WAN once a day. Due to the rate of change in the Exchange data store, the delta is normally about 800Mb. If you WAN could handle that or your delta (change in snapshot) is less. You could seed the remote site by snapmirror to tape, load the tape at the DR site and then start your snapmirror running.
If your question is can you run snapvault AND snapmirror on the same system, the answer is yes and recommended as best practice. See the nearstore documentation in the snap mirror guide.
Hope this helps.
Bren