Actually to rid an area of fireants completely you would have to spray with a very powerfully modified insecticide. It's designed to only rid certain species of ants, including fireants. I'd have to look up the name, but I know such a thing exists because I found an ancient container in a barn on our farm and asked about it...very scary stuff honestly. It may not even kill them all, just make them move off the field area...
As for chickens - I think most chickens should be smart enough to move away from a nest, or they'd just have a buffet. For small chicks I'd be wary - I've found small wild animal remains on top of nest before. That's in eastern NC where they get huge though! Not too sure though...never seemed to be a problem with my flock.