I've never heard of them but I'm not sure how useful they would be. The biggest issue is that spotlights on motorhomes are usually remote operated so that you can move the beam. These would have to be fixed (or at best have a very limited range). With 2 of them, the light might be pretty good as long as they are spaced on the roof (many mhs have 2 horns right next to each other). The other problem is that it would still be a pretty significant install as you'd have to remove the existing air horns, run electric wires (the air ones just run on air) and then replace them with these new combo air horns. Another factor could be the cost - from what I've seen air horns are a lot more expensive than spotlights and then obviously, if the air horns or the spotlight fails, you're stuck replacing both.
I guess for someone that has neither and wants both, this might be a good option but I think for most, separate might be easier / cheaper.