We use Dell's netvault product to do tape backups of our volumes. It works via the NDMP plugin. Doing the tape backup with NDMP gives us the ability to do single file restores as well as full volume restores. If you don't have any software solution to do this with you can hook a tape drive directly up to your filer if you have the right connections to do so and just do direct dumps of your volumes but I believe you lose the ability to do single file restores.
For our snapmirrors, we are snapmirroring the entire volume and not just the VSC snapshots. The volume was snapmirrored initially at the production site and then moved to the DR site to only have the changed data transferred. This allows us to quickly add our servers back into our vm environment and go at our DR site.