Found out that encryption is not available for OpenVMS clients for v5.0 or v6.0. Also confirmed with Symantec Support that it is not currently under development/testing either, and there are no plans, as yet, to include encryption functionality in the future. So I've submitted an enhancement request here:
We don't send media off-site, it all remains in the robots as we do cross site backups. I think the idea is that all traffic leaving a machine is encrypted before it leaves a server's (OpenVMS, Solaris, Windows) NIC.
You did the right thing in submitting an enhancement request. Companies in general tend to focus their energy into platforms that are in wide use and thus supply them with a good base. However, Symantec has a duty to fullfill the needs of the established customer base base as well. You've done the first step in documenting the need with an enhancement request.