I agree the hens are normally much more of a threat than the rooster. You are dealing with living animals so I can't give any guarantees, but a good rooster protects all members of his flock. Not all roosters are good, however. And I find that the dominant rooster is more likely to be protective. A non-dominant rooster can be as mean as the hens.
One risk is that the rooster (and especially the hens) may not see them as members of the flock. Other than dominant issues between two fairly mature roosters, you have two different types of aggression to deal with when merging new chickens. One is pure integration. Chickens can be territorial and may defend their territory from invading chickens. If you just plop new chickens of any age in the territory of a flock, they may try to run them off. I say "may" because this does not always happen. But this is the huge advantage of housing new chickens side by side but protected from the flock. They get used to each other and recognize their right to be there.
The other issue is pecking order. Older chickens will dominate less mature chickens. If a chicken lower in the pecking order invades the personal space of a dominant chicken, she has a right to peck that chicken to tell it to get out of her face. If she doesn't do that, she is giving up her dominant role. Usually, the subordinate runs away and all is well in the flock, but if the subordinate does not run away it is a challenge for status and can get ugly. Almost always, this is the hens and not the dominant rooster, but a non-dominant rooster can play this game. And it is usually the more mature chickens that are lower in the pecking order that are the most vicious.
A broody hen will wean her chicks anytime from maybe 4 weeks on. Those chicks are fully integrated in the flock but they are definitely lowest in the pecking order. They quickly learn to stay away from the older chickens. The younger they are, the more risk involved, but integrating young chicks can be done. I personally keep them in a grow-out pen until they are about 8 weeks old, then let them start free ranging with the older chickens. I think it is a lot easier if they have a lot of room to get away and stay separated. Different feeding and watering stations also helps avoid conflict. If space it tight, it is harder. You can help by giving them extra perches so the young ones can get away from the older ones, and give them places to hide under or behind.
We all have different circumstances so what works for one will not necessarily work for another. Sometimes integration goes so smoothly you wonder what all the worry was about. Sometimes it ends in disaster. You just never know until you try it. Good luck!!