NVIDIA has confirmed that their next proprietary driver update for Linux will introduce support for Vulkan rendering outside of the X.Org Server.

With NVIDIA's current Vulkan Linux driver it's not possible to achieve headless Vulkan rendering if the X.Org Server isn't running, but that limitation is said to be addressed by their next (post-375) driver release.

There is this NVIDIA DevTalk thread about a user unable to get Vulkan working on a headless server powered by four GeForce GTX TITAN X graphics cards, followed by other headless NVIDIA users chiming in that they too are affected by this limitation.

NVIDIA's Damien Leone then confirmed that this limitation is to be addressed in the next driver release. He commented, "Our next driver release will support direct to display which, even if you are not interested in presenting your frames, will allow you to use Vulkan without X running."