Is using ASM a pre-requisite for RAC?
i've found the definitive answer from the oracle docs

http://docs.oracle.com/cd/E11882_01/license.112/e47877/editions.htm#DBLIC109

in the Oracle Database Standard Edition and Oracle Real Application Clusters (Oracle RAC) section, it specifies

"Oracle Automatic Storage Management is required for creating and managing all Oracle database file types. Raw volumes, partitions, or third-party cluster file systems are not supported for storing Oracle database files with Oracle Standard Edition and Oracle RAC"