Oh so it's more like introducing two groups of chicks/juveniles to each other. That's probably going to be better than introducing chicks to adult hens. If the space in question is only a few inches, then they should be fine. I thought it was more like several feet. Good luck!
A picture would really help visualize this setup. Are the rocks too tall and potentially obscuring the chickens' vision? Or do they create distance between the two groups of chickens? I'm trying to understand why the rocks would be a problem. The goal is for the chickens to see each other...