Actually I have successfully connected my SurfacePro with 3 monitors using the surface dock.
2 of my monitors are connected using HDMI via the dock & the 3rd is connected directly to my SurfacePro using the mini-displayport to VGA adapter.
I'm restricted to enabling a 4th via my SurfacePro itself. It disables one of my monitors when I enable the SurfacePro as monitor via the display settings.