The dummy plug doesn't actually do anything except provide passive resistors where the video card expects them too be. It "pretends" to be a monitor.

You can buy plugs that pretend to be higher resolution than HD. I think this one pretends to be 4K.

For just remote controlling a computer that has no monitor, I don't see the point in trying to get beautiful graphics. What you want is to do your capture on there and then display your processed image on a machine indoors. That's where the resolution will matter, not on your VNC session to run mount and camera control.