There is a .NET DLL that is not documented:
C:\Program Files\Chaos Group\V-Ray\V-Ray 3.4 for Rhinoceros 5\VRayForRhinoNETInterface.dll
Adding that reference to your C Sharp project and viewing all the functions would be a good first step.
A few functions do not work in V-Ray 3, so if something doesn't work right away please post.
What are you trying to do and in what language? Maybe I can write a little demo up.