I have a Mac Pro 5.1 8 core Xeon with a Gigabyte Radeon RX 460.... and the game doesn't load at all.
Contacted support and they just shrugged and said that Xeon processors were not supported with Metal and had to be a I5 or I7 (WHAT?) and that they could not set up a test rig with such a config... and that the drivers of the video card were not from apple (WHAT ???? ).
Xeon Westmere has an exact equivalent i7 consumer version, the xeons are just of higher quality a rated for server use, so I don't understand there claim.
The RX 460 is exactly the same ATI chipset as the Radeon Pro 460 encountered in the Macbook Pro, just with lower tdp. No aditional drivers are needed, nothing is changed to make it work. Clean Sierra install and the video card works with no add ons, kext file changes, etc..
Great support.