This maggot feeding station just creates maggots for the chickens to eat. These would be just regular old fly maggots, as would be found in any exposed garbage, or laid in manure.
The flies lay eggs in the 'stuff' (say moldy leftover spaghetti) you put out for them, the females lay eggs there, expecting to be producing the next generation of flies. But the maggots crawl out of the bucket to pupate in the soil, and the chickens get them.
I looked up horse parasites and found this list of common ones http://www.diagnosteq.com/intestine.html but none of them seem to use garbage as part of their lifecycle. Bot flies seemed the closest, but their lifecycle doesn't involve garbage, either, as explained in this article: http://edis.ifas.ufl.edu/IG136
So, even if you have horses and chickens, and wanted to do this maggot feeding station, I can't see anything that would contribute a problem to your horses. The only possible result that I can see is some of the flies you would have in the area normally might use the maggot feeding station and end up NOT producing any actual flies because the chickens get them as maggots, before they pupate.
I can't imagine any of MY girls missing a tasty tidbit. Those beady little eyes don't miss much.
I knew some people who hung one of those bug zapper things in the corner of their chicken run. The chickens learned very quickly what that blue flash meant. I wouldn't go out and buy a zapper, but if I knew where an unused one was, I'd make use of it.
Meal worms seem very easy and cheap to raise.
Has anyone raised hatchery chicks on foods other than chick feed? How did you do it?