I use it for this as well. Have not had any coccidiosis and the ACV keeps that invisible slimey feeling down in watering devices. Have never had any problems with chicken health even using it in hot weather.I use it to make their guts acidic to help with parasites and what not. I take a shot every once in a while myself. For some reason I have always liked it.
I figure they get vitamins in the feed and veggies I give them. I do give them ACV with the mother every few bottles or so. It also helps keep the nipple watering system clean.