No matter what horse you put with him, there will be some sorting of a new pecking order. But, if you put him in with a horse that is also very dominant, you're going to have a much higher risk of injuries, not only at first, but it could happen at all times.
I like to seperate horses by gender; however, I was working with two dominant mares. They would come with injuries every few months that would lay them up for some time. I had to end up seperating them because even tho they knew eachother and had established a pecking order, they would always challenge one another. They were frenemies if I ever saw some; would beat eachother up if they were together, but will graze side by side along the fenceline.
This is what happens when you have democrats in office