If the shelter as large enough for both bunnies and is protected from the weather then it’s probably good. Pellets I don’t believe are necessary for rabbits as long as they have unlimited hay and fresh greens. Free feeding pellets is not so hot anyways, so it’s possible they do feed them once or twice daily. From what you’ve described, the only real concern I have of the chicken flying in is that that means there is no barrier wire on the top of the pen to keep predators out.
I keep my bunnies indoors, so I understand that for most of us it seems not so hot to see an outside bunny. I had a neighbor several years ago who had two bunnies in an outside run with their 5 chickens. They had a large enclosed yard with a large tree type house for all. There was stairs going up into it. I’d see the chickens and bunnies laying next to each other out there. There is probably a risk of someone getting hurt, but I never saw any kind of aggression between my neighbors rabbits and chickens. I definately would not of called it abuse. It was a very lovely yard for the animals, with lots to do. There was a small shallow pond, stepping stones, with thyme growing between them and the rest was mostly grass. There was a large tub of sand. They would go out and feed a ton a greens to the chickens and rabbits daily, mostly turnip and carrot tops, as well as a few other greens. If I was a rabbit I can’t say I’d complain about such a nice place.