I have two monitors and WME allows me to use either first or the second by selecting on of the two (same) gfx cards.
The image is displayed correctly on the first or the second screen, however the mouse is locked on the very first screen regardless of the gfx card selected so I can't interact with the game at all.
Tested on 1920x1080, dual monitor. Fullscreen.
Edit: Also it's set to extension mode so one huge desktop spanning two screens.