I can confirm that I installed using UEFI boot.
The systems are in use and I cannot test re-installing over BIOS boot.
For me the only issue was setting up openvpn using the documentation.
On my system the config was and is available on:
/opt/vyatta/config
I made sure that all scripts and config use this location instead of /config.
I also upgraded to newer release(s) (but not a recent one which might have a fix) and this location persisted with the upgrade.