You are correct. With the slotted hinges, you don't really need to drill the hole.

And if your're concerned about putting a pinhole where the hinge flexes, a way around that is to insert the hinge into one side(Let's say the wing), and pin through the wing and into the hinge. The whole point of using the pin is to make sure that the hinge stays somewhat centered. If, for instance, you have a solid aileron, and only cut the slot as deep as half of the hinge, you can fit the hinges into the aileron first (WithOUT glue) and then insert them into the wing. They can't slide deeper into the aileron because they are bottoming out in their slots.

And A BIG DITTO to what DB said. DO NOT glue them to one side first! (For the same reason he mentioned.)