To my knowledge, Bulgarov uses no grasshopper or Rhino. He likes ZBrush, and still uses the deprecated XSI.

Just like many of us here, he believes in the right tools for the job, which includes poly/SubD modelers, topology modelers and NURBS-- which of course is MoI. I actually started using MoI because of him. I'm sure there are many others.

He likes to "kitbssh" which you can do in MoI quite effectively. You may want to see my tutorial on it.

For the longest time he rendered in KeyShot, but had recently started rendering more and more using Octane.