If a SoC has a co-processor with proprietary firmware, potentially for things like security, remote management, bringing up the main CPU, etc, peripherals with

If a SoC has a co-processor with proprietary firmware, potentially for things like security, remote management, bringing up the main CPU, etc, peripherals with proprietary firmware, potentially with DMA access, or firmware operating at ring -2/-3, they can sidestep OpenWRT and you wouldn't even know it from the OpenWRT side of things.