in the

Symantec NetBackup ™ for

Oracle Administrator's Guide

...

Failover VIP exists and backup is load balanced

In this configuration, the NetBackup master server can always use the failover

vipname to reach an active host to run the backup script. However, becauseRMAN

allocates the channels on both hosts, the NetBackup media server must connect

back to the correct host to obtain the data for each request. Hence, the backup

images are stored under two different client names

Failover VIP is not available, and backup is load balanced, one policy

with custom script

A load-balanced backup without a failover vipname must overcome the combined

challenges of the preceding configurations. Because a failover vipname does not

exist, the NetBackup scheduler must attempt to execute the backup script on both

hosts and the script must start RMAN on only one of the hosts. Because RMAN

may allocate channels on both instances, the user-directed requests must present

host specific names so that the connect-back from the NetBackup media server

is able to retrieve the data from the correct host.

yes we do use that, gimme some time to fetch the script and get rid of sensitive information and I'll provide the RMAN we use with RAC

Please see appendix B of this guide http://seer.entsupport.symantec.com/docs/340131.htm.
There are 5 scenarios of Oracle RAC backup. The way of doing backups is highly depend on how RAC is configured.

Anyone can show your script? I want to see it as sample.