I've got polish chickens in with the rest of my "normal" flock. For the most part, they get along just fine. They free range during the days. I did have a white one that came as my rare & exotic with an order of rainbow layers (that's her in my avatar while she was healing up in the house), and even though she started off with them, they picked her head bloody and raw at about 5 months old. I got her healed up, put her back in the coop, and the next day she was bloody and raw again. I got her healed up again, and slowly re-introduced her back to the rest, and she was never bothered again. We have to remember that chickens aren't very smart, and they're going to pick at anything that looks different. As soon as her head was picked enough that they saw a little blood, they all went after her.
I have a polish rooster who is the bottom of the 3 roosters in the flock of 34 birds. His tail is usually fairly plucked, but his head is fine. As long as he goes to bed last and leaves the girls alone in the presence of the main rooster (a cochin bantam) he gets along fine. I had two other polish hens, a silver-laced and a buff-laced, and I lost the silver-laced to a predator. I don't know what got her, but something did. She had a very large crest and probably couldn't see the predator as well as the other girls. The buff-laced has a very small crest and no vision problems because of it.