I cover quite a bit of SSO related activities in my two part series. Here is part 1:
http://wahlnetwork.com/2013/02/04/successfully-installing-vcenter-sso-part-1-sql-database/
In a nutshell:
RSA_DBA is used for creating the schema (DDL) and requires DBO permissions. RSA_USER reads and writes data (only DML).
