This module is a wrapper around a native library and is meant to be run from standard Python (CPython). Rhino hosts IronPython which is a .Net (C#) implementation of Python and can only load .Net assemblies.
As @Alain pointed out, bulletphysics isn’t going work in the python environment for Rhino. That said, I do believe that @DanielPiker was able to get some python scripts put together that execute his Kangaroo physics library. Daniel, is that the truth or am I just confused?
Daniel Hambleton has also made his implementation of PhysX available. Depending on your needs, it might be functionally more similar to Bullet. Not sure about the GH/scripting options though.