Here you can find information on database security for the Oracle database running SAP systems. General information on Oracle security as well as information related to specific Oracle security products such as Advanced Security Option (ASO) is included here.
This paper from the German Oracle Users Conference (DOAG) discusses security issues affecting Oracle databases in an SAP environment, including Transparent Data Encryption (TDE) and Data Vault (DV).
This presentation from Oracle World 2008 gives an overview of Oracle Database Vault, including SAP certification, best practices, and performance.
A thorough security plan at your site must include securing application databases. This SAP whitepaper explains how best to secure SAP applications running on Oracle. Specifically, you'll learn about securing the OPS$ mechanism and securing DBA tools for Oracle including RMAN, BRBACKUP, and BRRECOVER.