In my setup I have 2 AMD Vega 64 graphics cards. Both cards are recognized by the system/driver. I can see them in the system page in the AMD Radeon Settings.
But only the primary card recognizes display port screens (have not tried hmdi). I do not have Cross Fire or any linking installed.
Is this a normal behavior ? In my mind the load on the graphic cards are better distributed when each screen is connected to it's own card.