Hi Steve - so ideally the export to the render engine would include vertex normals coming from the original NURBS surfaces.

Usually if vertex normals are supplied render engines will not do any kind of phong smoothing of their own with break angles where welding or not having welding is significant - those are all methods that render engines use to cook up vertex normals from plain polygons that did not have any vertex normals attached to them to start with (which could be the case in various situations like if you're creating polygons directly in a polygon modeling program or something like that).

That's what's so great about getting vertex normals to come through from the original CAD model - because when it does you don't have to worry about any of those kinds of phong smoothing / break angle / welding type issues... If the NURBS vertex normals come though it means the polygons will be shaded to look the same as the original NURBS surface even if they're completely unwelded with every single polygon unconnected to any other.

- Michael