Nvidia GPUs refuse to accelerate 3D w/o an output connected; if I had a Radeon, I wouldn't need the plug, it's just an Nvidia thing I believe.
Afaict, Moonshine relies on a separate graphical session running on your monitor and that's how it gets around that limitation of Nvidia GPUs. If I had a monitor plugged in to my box, Sunshine would work just as well.
It’s possible to make a fake display to avoid that; both Linux and Windows have this ability. No dummy plug is required (though it is simpler than software solutions).
I don't use the dummy plug for display, it's only that consumer nvidia gpus won't have working 3D acceleration if there is nothing physically connected to the card. My dummy plug doesn't support the resolutions I run games at anyway.
EDIT: Ok, correction, I bothered to go unplug the dummy plug and it still works. So I was wrong, Sunshine does not need a dummy plug at all, not even on Nvidia. Now it remains a mystery why I have one in the first place if it's useless after all…
Sunshine was significantly easier for me to get working using a dummy plug. I'm currently exploring other options but that's definitely the happy path.
Afaict, Moonshine relies on a separate graphical session running on your monitor and that's how it gets around that limitation of Nvidia GPUs. If I had a monitor plugged in to my box, Sunshine would work just as well.