My layer flock consists of 4 birds, 2 Barred Rocks & 2 Black Sexlinks. My replacement flock is a group of 6 Welsummers.
This has been the easiest flock integration that I have ever had...the layers mostly ignored the pullets. The only time there is conflict is when I show up with treats...the big girls want their treats and they don't like to share.
The flock boss, the most dominant bird, has established her dominance over the little pullets. They all know who she is and now she leaves them alone, unless there are treats.
I have a Barred Rock who is at the bottom of the pecking order in the layer flock. She seems to enjoy showing the pullets that she is bigger then they are...not a mean bird, she just has never had anyone bellow her in the pecking order.
So aside from little squabbles caused mostly by me, all us going well.
My advice is let the girls work through their pecking order....if there is no blood, there should be no problems. I will say this...integrating just one bird into a flock is challenging.