Have you ever work with  Oracle? :)
Is it RAC or Oracle under VCS?

See the NBU for Oracle admin guide.
Oracle RAC info in Appendix A.

If VCS or other failover cluster, install NBU client and agent on each node. Add the NB_ORA_CLIENT variable to the rman script:
ALLOCATE CHANNEL ch00 TYPE 'SBT_TAPE';
SEND 'NB_ORA_CLIENT=<virtual_name>';

This is RAC with 2 node.

I have heard the term cluster_config. When to use this ?

cluster_config is used to setup a clustered NetBackup Master or media server. This process is described in the NBU HA manual. The cluster_config script is used to build the cluster service group, install the NBU cluster agent and to move all catalogs to the shared drive.  DON'T runthis script if you merely want to backup your clustered Oracle instances.
All you need for your RAC RMAN backups is to read Appendix A of the NBU for Oracle (link in my previous post) and configuie your policies and scripts to use the virtual hostname.