I haven't used Nix. Kubernetes runs pretty well on all the Linux distros that I've come across - I guess this is because K8s itself runs most of its components inside Docker containers so K8s isn't generally prone to configuration issues.

That said, you still have to deal with certain host-level configs like file limits and such - So I guess for more advanced use cases something like NixOS could come in handy - I just haven't needed it yet - I'm running most of my stuff on Amazon EC2 - So I just make sure that my base AMI has the correct host configs for the kinds of use cases I deal with.