On top of everything else you should really know how to soldier. There is not a lot of room in a good UAV so all leads need to be short. Plus, if you're messing with a video system you should know a little about the longer range AV transmitters which cost more (of course). When messing with the higher freq's of these every wire length becomes very important as they can start to act like little antenna's causing interference and static.
Also mechanical engineering as in how will the UAV land? Will it belly land and break apart like the RAVEN SUAV? Or will it have it's own wheels like the Shadow, Predator, etc?
Also, a little knowledge about politics and laws is needed as I believe it is illegal in most states to control a RC airplane that can operate out of eyesight of the operator. Although I'm not 100% sure on that one.