In searching the help files, I found this under Datbase backup...
If you are using a full version of Microsoft SQL Server 2000 for your database, which is not installed by WSUS, you can use SQL Server Enterprise manager as an alternative to the Backup Utility. For more information about SQL Server Enterprise Manager, refer to your SQL Server documentation.
So I assume the asnwer is YES. You can use Full SQL as your database for WSUS. To find out more, pull down the white paper for Deploying WSUS.