Hi Jason,
Thanks for your question here on the forums!
Sequential rays cannot split within an NSC group – only the primary ray path is considered. Also, in Sequential Mode, a deterministic ray path is required, and only the number of rays launched (no more) may reach the image plane (ray splitting could potentially increase the number of rays which eventually reach the image plane). Because of the deterministic ray path criteria, bulk scattering is not possible either, as it would require a probabilistic approach.
You may read more about the mixed mode in this knowledgebase article:
How to model a mixed sequential/non-sequential system · MyZemax
Best,
Csilla