My chickens and turkeys have been living together and have been raised together for years. I've not had any blackhead disease in my flock. I even have my ducks and geese in the same area as the turkeys and chickens.
I did read a short thing online on it yesterday, after I googled it. I didn't read further because we don't have turkeys right now, sold them.I haven't looked for any sources online, I read about it in all of my chicken "how to " books. They warned against raising chickens and turkeys together. One book, which I really like, is written by someone who raises chickens, turkeys and I think also ducks all together. They free range together and sleep in the same coop at night. The book is called "The Chicken Tractor."
I think I'll ask around some more about this because I really would like to add turkeys to my flock.