NetBackup can be installed anywhere on the system. It can be installed directly on the /usr folder. It usually is NOT because of growth concerns. It is not a good idea to have it directly on /usr because the growth potential to 100% of the available space would put not only Netbackup at risk but also everything else on the /usr filesystem.
Listen to Stumpr....
the images and databases get very very big, some people have over 100 gig.
you don't what that on your /usr file system.
you might not even want that on the same drive as root.
most people create /opt on a different drive, then link /usr to /opt. this way if /opt fills up ( because I was not doing my job and watching disk space) I will not kill the server, just /opt.