I'm currently researching this very thing. The standard advice seems to be not to do it, because chickens carry a protazoa that is harmless to them, but deadly to turkeys, causing a condition called blackhead. The broad-breasted meat breeds seem to be more fragile than the heritage breeds.
I may not have all my facts perfectly right there, but that's the idea. That said, there ARE people who do it, and I'm going to try to raise chicks and poults together this spring. Check on youtube for turkeys and chickens, and you will find some coexisting very peacefully. There are, however, risks...