The Impostor would not be able to shoot the Dart Monkey. As soon as it sees the Impostor taking out their gun, the Dart Monkey will try to avoid getting shot. The Impostor doesn't have any experience shooting at moving targets, presumably has a limited amount of ammo, and would likely have to deal with the Dart Monkey using the trees to make things even harder. The Dart Monkey on the other hand, shoots down moving targets for breakfast, has a seemingly unlimited amount of ammo, and will immediately lead with darts. Plus, the Impostor has baseline durability, meaning they probably can't too many hits.