Thanks for contacting us, we hope you enjoy using RailClone. It is indeed possible to nest styles. All you need to do is select another RailClone object as the source for a segment.
If the nested object has randomisation you'll also find a "nested" checkbox in the segment's settings that ensures the randomisation cascades through the style. (Note though that this disables instancing).
Finally, if you plan to add a style like this to the library you should make sure that the nested style's size is set using the X and Y size parameters and not splines because these aren't imported by the library browser. If you're not planning to add the style to the library you needn't worry about this limitation.
I hope that helps, please let me know if you have any further questions.