OK here is some clarification.
When you create DWF / DWFx through the UI you are presented with a Printer Setup like dialog which allows setting of vector or raster.
The DWF / Dwfx created this way respect the choice of vector unless the view has shadows etc when you are shown the usual pop up about raster printing and a raster format file is created.
If you open a vector DWF / DWFx in Navisworks and select something then the Revit data properties are displayed. For example a door will show its height, width, fire rating, GUID etc etc.
If the DWF / DWFx is raster then none of that comes through and the intelligence is lost.
Unfortunately the default when creating through the API seems to be Raster format and it's not obvious if any of the setup parameters for DWF / DWFx export will force a switch to vector or if changing the print manager setting for hidden lines to vector (which is what the UI is showing as the control method) will have the desired effect either.
We are required to produce the vector format "intelligent" files as part of our BIM protocols, exporting via the API helps us produce files with the correct naming format.
Thanks