There are five of them total that I know of, 4 tied to late game campaign missions and one just north of the hunter HVT.
They look like how the grey guard are described, To those who don’t know these guys where Atriox’s guard. Now they seem to be really tanky brutes that can tank 6 headshots, or a lot of ordinance.
they also have unique moves with both the scrap cannon and gravity hammer.