Hello,
you have to install DP localy on the cluster member. Map a network drive to DC-Cellmanager\omniback and run setup from the x8664 folder. The setup will detect the cluster and install DP cluster aware.
Configure the backup to point to the virtual server, all other settings are the same to a physical server.
Do you want to take a LAN or a SAN backup?
If you want to take SAN backup you must zone your library to the cluster nodes. The library is the available to the virtual servers.
Thomas