diagrams-opengl is unmaintained. Do as you like with the code.
Eventually OpenGL should render both 2D and 3D Diagrams. The 2D works now, but there's a fair bit of work making it less buggy. Right now, for 3D, your best bet is the POV-Ray Backend.
If you want to contribute, there's work to be done both on the OpenGL side (writing shaders, translating the 2D Haskell code to 3D) and on the library design side (adding 3D primitives and useful functions for working with them).