Haven't heard the Vulcan mentioned in a long time. My experience with them was less than complimentary. It would move a lot of metal in a short amount of time, but much of it just sprayed out at random. The seeking radar was one of the most powerful ever made for a ground mobile unit. But it couldn't track for shyte. The Vulcan was good for clearing ground clutter, but as for hitting and stopping anything in the air, pretty useless.
For the drone, it's like any other surface to air target. Get a lock with a missile and let it fly. I would think that the radio link to the device would be the weak link, so I would try to come up with some jamming around the carrier freq used to command it. One doesn't need to actually take over the command/control freq to succeed, just jam it so that the drone will fall back on it's failsafe internal mode, whatever that is.