it doesn't export geometry directly into the rib, it uses something like a run program procedural to call an external program to generate the geometry on the fly
on windows it calls a .dll or .exe file, on linux it calls an .so file

a sample line (on windows) is here:
Procedural "DynamicLoad ...

Massive can render with prman, 3delight, air, etc by using a runprogram procedural.
Since octane will have rib support, will it be able to support rendering that sort of thing?