Yes and no.

Increasing this question is being asked because the SAP agent is discontinued in BE 2012. Since SAP is based on either SQL Server or Oracle, can I back up the SAP database using the SQL or Oracle agent?

Yes, if your SAP database comprises one SQL or Oracle database, then you can backup the database using the appropriate agent.

No, if your SAP database comprises more than one SQL or Oracle databases.  Although you can backup the individual databases using the database agent, you might end up with a logically inconsistent database when you restore them.

Suppose your SAP database comprises database DB1, DB2 and DB3.  There might be a transaction TransA which updates DB1, DB2 and DB3.  When you use the SAP agent, it is aware of the entire transaction.  When it backs up the SAP database, it will make sure that the updates to DB1, DB2 and DB3 are backed up together.  When you do a restore using the SAP agent, it will restore all the updates to the various databases, so you have a logically consistent database.

If you use either a SQL or Oracle agent to backup the individual databases, these agent are not aware of the transaction spanning the three databases.  Each database is backed up as if it is a stand-alone database.  Due to the timing of the database backups, you might have a backup of DB1 and DB2 with the updates from TransA and the backup of DB3 might not have the update from TransA. When you restore the databases from the backups, then TranA will be incomplete and the SAP database will be logically inconsistent.

The above argument also applies to Sharepoint farms which comprise more than 1 SQL database.  For these farm, you would need the Sharepoint agent to back up the farm.  Using the SQL agent to backup the individual databases may also result in an inconsistent Sharepoint farm after a restore.