Re-reading the tech manual, it does seem theoretically possible to use the PVD for landing, but you would have to push the PVD selector button below 5ft RA for it to unshutter. You cannot 'arm' it in the air.
Eck, does your tech manual mention the Rollout PVD inhibit found in our manuals?
Rollout mode, according to autopilot/FD notes in one 747-400 manual, includes LOC mode (ROLLOUT un-annuciated) on the PFD, so the PVD may be inhibited during Autoland and FD-guided landings.