I am getting ready for my first chickens and was wondering the same thing.
I have used Borax and sugar (in lidded plastic containers with holes punched in them) effectively to get rid of ants. It takes some time to get their numbers down but they can be lured away from areas they are not wanted pretty quickly.
How harmful it is for to chickens to eat the ants? I do know good soil should have some boron in it. So, for now, I am going to make the assumption that, if you lure the ants away and keep the coop and all areas hens will graze free of leaves and debris ants love to nest in, the hens will be ok.
Once a week I pass Cornell University of Agriculture. I will stop in and pose this question.
In the meantime, if there are any chicken loving vets reading this thread I'd love for you to weigh in!
One last thing, ants play a role in decomposition so don't be too eager to completely eliminate them.