Theoretically, nvidia.ko never comes in the same dvd / usb-stick / download as the kernel, it's always a separate piece installed by the user later (even if with a helper program). "Super Easy" derivatives of mainstream distros may include nvidia.ko (and libdvdcss etc) in the initial install, but mainstream distros including ubuntu do not. So they could say, if there was some violation of license going on, it wasn't them doing it, because they were not distributing something derived from the linux kernel. They may separately offer some "shim" code and binary under a separate license that the user then combines with the linux kernel headers on their own machine, and does not distribute the combination.

That's one of the attempted justifications anyway. So what's more "audacious" here is Ubuntu distributing zfs.ko included in the initial install, and not requiring a dkms-like setup.

There's disagreement, even among core kernel developers, about whether nvidia's binary kernel module is OK. The fact that they've gotten away with it for a long time doesn't mean that it's OK, just that it's somewhere between hard and impossible to enforce copyleft (for various reasons worth of a separate post). ref: https://lkml.org/lkml/2012/8/1/411