In reality, you usually shouldn't be getting so close to a poison ivy plant so that you are looking for the aerial roots if you are trying to identify a plant and figure out if it is poison ivy or not...
If you spot aerial roots on a plant that has all of the other characteristics of poison ivy, then you can be sure that you have correctly identified a poison ivy plant. They are not usually easy to see though, so don't use the roots as one of the main things you look for though when trying to avoid poison ivy.
