I think is just the standard requirement for valid RAIM during the GPS approach.
And valid RAIM will require the baro input if you short of that one satellite.
This is how it works in the USA, AIUI.
Whether you need RAIM for enroute (where BRNAV is a requirement i.e. FL095+ airways) I don't know, but I very much doubt it.
In none of these situations is the altitude part of the GPS solution used to suggest where the plane should be vertically.
A RAIM prediction is done purely on satellite constellation geometry, taking into account any duff satellites, and your location. Atmospheric pressure doesn't come into it, AIUI. There are even websites which will do it for you.