I had thought NetApp's SnapManager for SQL was going to switch from VDI to VSS when it supported SQL 2008 backups. I've reviewed the BP guide, the release notes for 5.0, and the Install and Setup Guide for 5.0 and I see no mention of VSS.
Does the SnapManager for SQL still use VDI (Virual Device Interface) for SQL 2008?
At this time SMSQL 5.0 still uses VDI to quese the SQL databases in SQL 2008. Looking on the new NetApp Field Portal (http://fieldportal.netapp.com) and searching for SMSQL in the quick search you will find a SMSQL Techincal FAQ where I found the answer that is still uses VDI at this time.