Do you have the Linux cluster installed as such within Data Protector? Is it a MC/Serviceguard cluster? This involves installing the DB2 component on each physical node in the cluster, then, importing the Virtual Name. The procedure for this is in the Installation and Licensing Guide
However, looking at the DB2 Integration Guide, I did not see any provisions for being in a cluster. You can try inporting the Virtual cluster name, and using that as the hostname of the DB2 integration,, but, I see a real chance that you may need to back the cluster nodes up individually