Not a problem with this method of integration. The chicks will be able to handle any bullies by racing back into their safe pen where you will open chick-size portals only after they reach three weeks of age. By that age, they understand the danger some adult chickens pose and they are more than able to outrun them. In fact, watching tiny three-week old chicks outwit an older bully is high entertainment.
However, the amount of bullying under this system is naturally limited due to the fact that the adults do not see the chicks as intruders, the way they would if they were suddenly introduced at a month or two of age. When adult chickens watch chicks growing up right under their beaks, they tend to view them as flock members, not outsiders.
In fact, with my two sets of chicks raised under this system, there was zero bullying by the adults. The bullying came from the juveniles bullying the second batch of chicks, and it hasn't been anything worse than four-month olds thinking it fun sport to chase babies. The way the safe pen is set up with small portals and the same portals in the other partitions in the run, no baby chick has ever been caught by these juvenile sports.
