Assuming the LineStrings are digitized in the correct order (start point is most elevated), running
SELECT ln.<id> AS ln_id,
dmp.path AS vtx_id,
ST_Z(dmp.geom) < LAG(ST_Z(dmp.geom)) OVER(PARTITION BY ln.<id> ORDER BY dmp.path) AS is_valid
You probably don't have to export the 3D view. This is just a visualisation. The source data is what you want to be looking at. Am guessing that your source data is going to be a Digital Elevation Model (DEM) or TIN. Possibly a raster gridded dataset might be suitable also.
All of this will of course depend on what Rhino can support as an input file.