NRaas SP has two occult functions relevant to this discussion. One is that under EA standard, sims pick up random occult states throughout play, for no real reason, in most if not all worlds. There is no way to control that. When running NRaas SP and having its progression in control, sims can only gain occult states for a good reason -- they are born (having inherited the state from their parents or possibly grandparents if so allowed through the mod's options), immigrated in, or spawn that way to begin with (as with homeless NPC Service and Role sims), or some event happened in-game to "turn" them.
The other is the Occult Ratio setting mentioned. That one caps the occult population in town by each occult state so that if the cap is reached or exceeded, there will be no further births or automatic SP immigration of resident sims with that state until some of those occult sims lose their occult state, move away out of the world, or die. But one also has to be running NRaas SP for progression, not EA's, for those caps to be in effect.