It seems that you can either have rounded edges OR Smooth shading (Smooth overrides Rounded Edges) and Rounded Edges don't care about the angles between faces.
Here's my test (and the difference in shader settings):
And the same scene in Octane Standalone:
It seems that you have two options:
- Use different materials for different objects/meshes (one for Rounded Edges, one for Smooth)
- Use a bevel modifier on the object (giving you control over which angles should be beveled)
NB: Rounded edges doesn't work with Auto Smooth..