Interestingly, Apple was on the list of the initial Vulkan backers — but they pulled out at some point before the first version was released. I suppose they saw the API moving in the direction they were not interested in. So far, their strategy has been a mixed bag. They failed to attract substantial developer interest, at the same time they delivered what I consider to be the best general-purpose GPU API around.
Regarding programmable tessellation, Apple's approach is mesh shaders. As far as I am aware, they are the only platform that offers standard mesh shader functionality across all devices.