Migration of oracle database from rhel5 to rhel6
The database[s] and software are on SAN/NAS storage. In that case you can remount them on the new server with the same path's. Because the OS version is different issue a relink for the Oracle binaries. Don't forget to also copy /etc/oratab, /etc/oracle and /usr/local/bin files etc.

Backup and restore are not bad at all but assuming there is some pre production environment with similar setup, you can use that to verify the procedure before the production migration. This is the quickest option (remounting).