SQL server Standard and Enterprise 64 bit and 32 bit 2012 are the only ones supported for vCenter 5.1 U1.
There is a small change here:
- Take a snapshot of current vCenter 5.1 and 2008 sql db VM.
- Upgrade the vCenter 5.1 to vCenter 5.1U1.
- Once the upgrade is successful, consolidate the snapshots.
- Backup the vCenter 5.1 U1 DB on SQL 2008.
- Build a new vcenter server pointing to a new SQL 2012 DB using the vcenter 5.1u1 install CD.
- Restore the SQL 2008 DB to SQL 2012.
- Reboot the vCenter Server.