Im not sure I entirely understand the question, but afaik Vulkan is always used as an intermediary when using dxvk (source: my own personal experience + _winery_whats_the_difference_between), because dxvk is a translation of directX(9-11) to something the host operating system can understand, e.g. Vulkan, hence the need for the Vulkan dylink library, so macOS can understand what your trying to ask the graphics API (metal to do).