Hi
I don't use dummy plugs, not on the H81 Pro btc boards, AM1 boards, F2A88X boards, Z170 Boards.
both with RX480 and GTX 1060 / 1070 and 1080 (everything on linux, of course

)
there is a trick to read the EDID from your monitor, save it to a file, and then feed it manually to the X window, so it will not check if the monitor is present or not, which is great when you wanna control fan speeds, overclocking or enter remotely via VNC, because the OS thinks the monitor IS connected

if there is interest i can find my notes how to doit, and post it.
BTW: I did that mod with the VGA-DVI adapter back in 2013 when it was necessary to do it, but nowadays makes no sense because there are no more analog GPUs, all modern GPUs has DP / HDMI / DVI-D only, no DVI-A anymore.