Only sort of, quoting this article

much of the important graphics code isn’t actually open-source. Nvidia appears to have moved much of its proprietary code into the firmware on its graphics cards, which the open-source code interacts with.

So while they did ‘open source’ their drivers, theyre also not accepting contributions that aren’t in house. The codebase is too locked down to benefit other projects like NVK, as a true FOSS project would be.