It is possible to map a 1:1 relationship between multiple monitors on VNC Server and VNC Viewer, ie. VNC Server's monitor 1 displayed on VNC Viewer's monitor 1, VNC Server's monitor 2 displayed on VNC Viewer's monitor 2 and so on.  

To do this:

• Check "Full screen mode" in VNC Viewer > Options > Advanced > Display
• Set "UseAllMonitors" to True in VNC Viewer > Options > Advanced > Expert tab.