NVK itself is not dependent on anything proprietary, but it's practically required to enable NVIDIA's GSP firmware blob if you want to see actual performance since it's what enables re-clocking (older post by Collabora here which touches on it).
Slight correction, it's available in Linux 6.7, and has to be enabled with the kernel parameter nouveau.config=NvGspRm=1. It may be enabled by default soon though (latest news I could find about that here).
NVK is a new fully open source driver for Nvidia GPUs. Derived from documentation & official FOSS code drops from Nvidia, unlike the legacy Nouveau driver which was mostly the product of reverse engineering proprietary drivers.