I hate fighting bunnyhoppers who use shotguns, and I don't personally use it exactly as people would think.
While I do jump, I use the surroundings hugely to advantage. Hense why I love Waverider, it has little ledges and all sorts of crap you can jump onto and jump off of. I often strafe to one side or the other and jump onto an object, when I hit the object I turn and shoot. Repeat until opponent is dead or until you're at low enough health to retreat.
I use the snowbanks on Snow Valley to launch myself into the air, above other players.
Railings, anything that stands out. Think Parkour. If people can't figure out where you're going then it's very difficult for them to shoot you.
Bunnyhopping is pure luck, hoping they don't shoot you. If they're farther than about 20 feet away, it's an easy shot anyway.
It's a shotgun's tactic, which in my opinion, is a noob's tactic.