Of course, this is not well documented so I understand that someone who isn't knowledgeable about NixOS would presume like the author that they had to depend on a Linux kernel to get these userland packages. Even I can't say with 100% confidence that everything packaged up under linuxPackages has a kernel agnostic version derivation for its userland components.
I remember being very skeptical of NixOS when I first started using it and it seemed like it was trying its best to prove me right. It really was my dislike for Ubuntu that motivated me to go all the way.