Caporegime
According to Ryan of AnandTech, the Primitive Shaders are Enabled.
https://forum.beyond3d.com/threads/amd-vega-hardware-reviews.60246/page-45#post-1995903
Q: According to Compubase.de, primitive shaders are not enabled on RX Vega yet.
A: FWIW, AMD told me that they are enabled.
https://forum.beyond3d.com/threads/amd-vega-hardware-reviews.60246/page-45#post-1995903