UniFi Video - Can I use the VGA/HDMI ports on the NVR appliance?

No, because the NVR appliance does not have an X windows layer. The Debian server is headless. Theoretically you can install extra Debian packages to run a stand-alone browser, but it is not recommended—it will saturate the CPU and RAM.
 
Connecting a monitor and keyboard provides command-line access only, and is only necessary when upgrading/reinstalling from an ISO image.