Hhmm… after watching the films, cartoons, etc. and seeing the physics of all this, I would think that yes, the proton gun would “do the firehose thing.” Although, thinking about it, proton packs shoot proton beams. The properties of which are obviously much different from water out of a hose, or bullets from a gun. So after giving it a little thought, I don't really think that proton guns would produce any sort of recoil. I think because firehoses and guns deal with compressed kind of potential energy…. I think. In firehoses, you have pressurized water that (with the switch of a valve) is released, and “pushed” out of a nozzle, turning to kinetic energy. With the proton gun however, there's no compression, thus when the proton beam is produced, nothing is being “pushed”. I'm guessing it's sort of like a flashlight maybe. If you turn on a flashlight and set it down on it's own, the force of the light beam doesn't cause any recoil and push the flashlight backward, because light works like that. I'm not a science guy, but I'm guessing because this kind of stuff works on a micro level, with particles and things. The particles just aren't massive enough to force anything, at least not anything heavy. Maybe if proton packs weighed .000000000001 grams or so, then that recoil firehose thing would happen.
I really don't know however. For one, proton beams as far as I know don't exist so it's hard to explain that with science. Plus, I'm not all that smart with science.