Particle systems can now be exported as a native Arnold points primitive. Their type (Disks, Spheres, Quads) can be set from the Arnold Properties

Pflow particle systems can pick their shape through an Arnold-specific node called Arnold Shape. If selecting a standard shape, each particle is replaced by an instance of the shape. Also, you can select Arnold-specific primitives such as Procedural, Alembic, Volume, and lights.