A snapvault destinations is readonly, therefore moving a lun will not work. What will work is creating a clone of the lun with the "lun clone create" command (no extra licenses required):
1. Create a qtree in the same snapvault destinations volume the original lun is in.
2. Create a clone of the lun in the new qtree:
lun clone create /vol/<sv dest volume>/<new qtree>/<lun> -o noreserve -b /vol/<sv dest volume>/<sv dest qtree>/<lun> <snapshot name>
3. Use ndmpcopy on the clone.
4. Destroy lun clone.
Snapvault updates will work while the clone exists. Only note that the clone will exist in any future snapshots and that snapshots will get locked.