With a broody hen I wouldn’t do it any other way. Hens have been raising chicks with the flock since there were chickens. It’s the normal natural way. There are risks no matter how you approach it, bad things can happen to living animals. But to me, the benefits of a hen raising the chicks with the flock far outweigh any risks.
If a rooster is introduced to the chicks soon after hatch, he normally accepts them as his and is very likely to help the Mama and protect them. Each chicken is an individual and each flock has its own dynamics, but a rooster protecting his chicks is pretty natural though not all do it. I’ve yet to see a rooster threaten a chick that was raised with the flock until that chick is a cockerel starting to challenge the rooster. Then you will possibly see some threatening, though even that is usually in response to a challenge or the cockerel bothering his hens.
Another hen might be aggressive toward the chicks, especially if they leave Mama’s protection and go wondering through the flock. I’ll emphasize might. It’s pretty rare for any of my hens to really threaten a chick. They might peck a wayward chick, teaching it that it is bad chicken etiquette for that chick to enter the personal space of its social betters, but the chick just runs back to Mama when this happens, maybe having learned an important lesson on how to act in the flock.
A fairly common occurrence. At about two weeks of age a chick leaves Mama’s protection and goes to stand with other hens around a feeder. Sometimes the hens ignore that chick but usually a hen will eventually peck the chick, reminding it of proper flock manners. The chick runs back to Mama as fast as its little legs can carry it, flapping its wings and protesting loudly. Mama generally ignores this behavior. But if that hen starts to follow the chick as it to strengthen that message, Mama politely whips butt. Nothing threatens her baby!