if you treat the glideslope almost like a localiser approach i.e. check various altitude points against the charts then you can confirm that the two match up.
If there was anything to take away from the video, it was that. Checking at the FAF at platform altitude with a fault as described will not reveal anything. Even at the marker, you might be unlucky and be at the correct altitude but on a steeper glideslope that will intersect the terrain short of the runway.
An RNAV-to-ILS approach is just as vulnerable as it would all check out until after you’d been coupled to the glideslope for a while. The RoD, power and pitch could be close enough to normal not to stand out, especially with changing wind or turbulence.