Sounds like what you want might need is to install netbackup on each node. (For those that think this is what you would normally do in a cluster - no not on Tru64 cluster - only need to install once to a shared cluster disk)
The installation would have to be done into the member specific disk areas of each node, this would occur by creating softlinks into this area for the base directory /usr/openv/
What you are trying to do is kind of complex/messy IMO, and what we faced doing when we could not get Netbackup 6.0 working straight out the box on our Truclusters as a failover media server. Veritas had changed the way of communicating via VNETD and had to get support to help fix this.
See my previous posts for solutions in Tru64 clusters.