Seems to support arbitrary resolutions (I just started the game up and it was displaying across all three monitors). However, UI is odd due to the scaling, so the UI thinks your vertical res is twice as high as it actually is due to your settings. Text boxes are visible, the game is totally playable, but characters faces and stuff in their portraits while in conversation are cut off.
Otherwise, the HUD is at the edges of the screen, which is how games that don't normally consider multimonitor act normally.