Given the wording of "drive units, and its battery management system" I'd think the BMS is linked to the drive units and under the same ECU. I'd assume the drive units and BMS are tightly integrated, as that's basically the entire high-voltage system and you have to manage the two-ways energy flow between the two (propulsion and braking / regen).
Not really, the FOC software that runs on the inverters is compute heavy and safety critical. It gets its own dedicated controller (they are actually running to cpus in parallel in case one fails) and same with the bms. They talk over can currently in teslas. bms states it’s max charge and discharge current, and everything else listens
Am I reading this wrong, or are these actually five categories?