KeyShot just has problems using round edges with polygon models, and it doesn't work with NURBS. Consider these 3 exports: 1, 2 and 3-- each of varying degrees of tessellation with the first being less and the last being the most (very much as an STL file gets tessellated when importing to KeyShot). I typically try and export my models to look more or less like #2 with medium tessellation density.



Now consider these renders in KS.



1. Shows the wireframe of each version in KS

2. Shows the max rounding corners (1). None of them do well at all.

3. Shows a decent rounding corner setting of .04 on the least tessellated model

4. Shows the same rounding setting of .04 on the most tessellated model

NOTE: Both show artifact. Perhaps there are a bit more on the less tessellated version, but not by very much.

5. A very small rounding setting of .01 of the most tessellated model. Still there are artifacts.

The round edges isn't perfect and IMO works best a very small setting with medium tessellation. HTH.