Doubtful. RAM wouldn't waste money, time, and resources developing an active component to make fuel mileage worse. There are hours of wind tunnel runs performed when vehicles are designed and checked for aerodynamic drag. Small changes can make a noticeable difference in drag. If the AAD did worse in testing, they wouldn't have used it as it adds unnecessary cost, weight, and complexity for a negative gain. Cost being a driving factor where, for example, 100k trucks are built with AAD at $100 each = $10 million in savings if they deleted it.
While the aerodynamic difference is obviously not a dramatic increase, it works in combination with other factors to achieve a measurable increase in fuel efficiency. When RAM is competing with other builders, every little bit helps. And there's a proven history of wings, moldings, under-car panels, etc. being used on high performance race cars like F1 to improve aerodynamics - it's not dramatic from car to car, but it makes a small difference and can be the factor that determines who takes the checkered flag.