Yeah the reason SC isnt deleting any snapshots is that the snapshots are not named sohp16gdcvi1302-hourly-20110913154000 instead they are named smvi__sohp16gdcvi1302-hourly-20110913154000_recent__20110913154037.
SC does not support any naming conventions other than it's own.
You can try updating smvi.override so that smvi doesnt change the name of the snapshots
Add in smvi.override :
snapshot.name.format.timestamp={backupName}
But other than that I cant help you further
Maybe talk to the smvi folks or snapdrive folks?
Keith