yes Dou, from what I have read and heard from others with them, the higher percentage onagadori blood a non molter has, the more of an issue with isolation. A normal nm phoenix type bird will be ok just in a pen by himself but best with no hens.
The higher the percentage goes, the more isolated they need to be IF you want him to reach his fullest potential.
Anything that would trigger testosterone levels to spike, will also trigger molting in them.
So yes a pure onagadori should be out of sight and sound of all birds, even crowing roosters. But just to test a nm phoenix, a pen away from hens will be fine.
Again, this isnt first hand knowledge on my part, just what I have read and had those with them tell me.
That being said, the white male I have from Cy has been in a breeding pen for 2 years, since I got him as a yearling. He's in hard feather finally now, but has never molted since he's been here He'll be 3 this spring.