The sad truth is the license of non-GPL Linux kernel modules is very rarely cared about nor enforced. There are ton of embedded devices that don't bother with the NVIDIA shim scheme but ship with straight proprietary .ko:s on the device.

Since it is a distribution by a hardware vendor that ships NVIDIA GPUs, I'll assume that they got a licensed from NVIDIA to ship their operating system with the proprietary drivers.

Possibly, but what about the license of Linux? Surely nvidia.ko (being a derived work of both the GPL-licensed Linux kernel and the proprietary NVIDIA kernel object files) is non-distributable? Otherwise why does every other distribution faff around with akmods/DKMS, etc?