Night vision works well even without a moon. A full moon looks nearly like dim daylight, but you can still see very well with only starlight. Weapons with thermal imaging sights don't work off ambient light at all, but rather sense the heat differential between the ambient air temperature and various objects in the landscape.
If we have night vison devices and they(the enemy) don't, it's definitely to our advantage to have a moonless night. That means they are relying soley on available light- in other words they're nearly blind.