Hi,
As per our understanding of the issue,
From the information provided, it seems that you cannot backup database on the SQL Server and you get the following error message " Final error: 0xa0008443 - One or more SQL Database consistency checks have failed".
The issue you are facing has nothing to do with Backup Exec. The Database Consistency Checker (DBCC) utilities are a collection of programs used to verify integrity of databases. Apart from checking the logical and physical consistency of a database, they check memory usage, check performance statistics and can repair certain database errors. The consistency check that is run is actually a part of the SQL 2000 program and Backup Exec merely triggers the consistency check. Please try running DBCC manually through SQL 2000 and check if it reports some error. Then try running the DBCC within Backup Exec without including the indexes. If the DBCC is successful, try running the Backup Job again with SGMON running in the background.
Note: Start sgmon before starting the Backup Exec/backup/restore operation.
For more information on SQL Consistency Checker Utility please refer the following technote http://seer.support.veritas.com/docs/242004.htm
We hope this will help. If the problem still persists please revert back.