I'm just speaking from the perspective of the spec, which defines surfaces and swapchains as extensions that are never guaranteed to be available, so a complian

I'm just speaking from the perspective of the spec, which defines surfaces and swapchains as extensions that are never guaranteed to be available, so a compliant driver may work in the absense of any kind of GUI by just reporting those extensions as not supported. Whether your Vulkan driver actually supports running in a headless context is another question though, and of course the Vulkan software you're trying to run has to gracefully handle the case where surface/swapchain aren't available.