That monitor has a separate composite and s-video input, so you could ostensibly hook up two cameras to it directly, and use its own input switch to determine which camera's image to see.
You will be completely fine with just one, unless the two cameras are miles apart. Most field monitors have an A and B input to switch for that very reason. As well you are asured that you can campare the to images correctly, without worrying about the monitors being calibrated.