Orbis doesn't work the way you think it does. The kernel is based on FreeBSD, but the entire gfx stack (and everything else above the kernel) is custom. It's not even OpenGL compatible, instead running their custom GNM library (Metal/Vulkan/Mantle equivalent) and GNMX (OpenGL/DirectX equivalent).

Nothing they've built in their stack would translate to an Xorg driver, beyond the kernel shim (the smallest and simplest portion of the code, in most video drivers).