may be you can try to configure using the one active node and check if that work...i dont fine it even it work or not.. so trying is the only option that i feel.
even it work, it is not the ideal/recomended way to configureing.. RAC backups always needs to configure using the cluster name not with node name.
because if database is moved/accessing though another node, backups will fail from the first node, also restore is not possbile from the 2nd node.
below extract from netbackup for oracle admin guide 7.6 page 194
Warning: Do not use a single virtual client name if the backup is load balanced
across more than one node. In a load-balanced configuration, the node that hosts
the IP address to which the virtual name resolves, generates successful backups,
but the jobs originating from the other nodes fail with status code 54.
If a virtual client name is not used, a regular restore can be performed only from
the node that is associated to the client name that is specified on the backup.
Another possible solution in this environment is to use an alternate client restore.
