Hello,
1 : SQL Instance on the SBS Server with TAPE Drive connected to SBS: In this ase you will require the SBS License for Backup Exec which will include Exchange, SQL, IDR, AOFO License.
2 : SQL installed not on the SBS server but to a different server and TAPE Drive connected to the SQL Server. Backup Exec only support TAPE Drive connected to the Backup Exec Server.
Hope this helps...