I would not worry much about the distinction. Patterns are simply about communication, they should not be a straight-jacket for your design. That having been said, the following two links describe the differences:
You are correct that ActionServlet is a front controller (tho I would say more generally that Struts itself is the front controller). No, you are off base with your application controller example. An application controller deals with page flow and view dispatch logic that spans requests, ala a wizard that takes you through a series of screens to complete your task.