Have now succeeded in restoring a file to the client from the offsite Puredisk storage. However to achieve this I had to build a master server with a different name from the original master, install the PDDO and set up communications with the offsite Puredisk server. I then had to import the images from the Puredisk server into the new master server catalog and update the client to allow communication with the new master.
At this point I was able to restore files to the client.
I was led to try this approach by a paragraph on page 531 of the Netbackup 6.5 Troubleshooting Guide which states "Disk based images residing on SharedDisk, AdvancedDisk or on OpenStorage disks cannot be recovered by means of the Netbackup catalog. These disk images must be recovered by means of the Netbackup import feature". It struck me that this may also apply to Puredisk images.
If this is the only way that it is possible to restore from offsite Puredisk storage pools when the original master and the original storage pool are lost then that's fine but it seems kind of cumbersome so I've left the support call open to see if there's a cleaner way of doing it.
Anyone got any thoughts?