I was wondering if roosters a a treat to new chicks in a coop
Any adult flock member can be a threat, but there is no way to know which individuals will react which way until you expose them to the situation. I have seen more intolerance from hens towards the chicks in the flock then I ever have seen from the roosters, but each bird is different
If you want to have a broody raise her chick within the flock then you have to be very observant of the flock's behavior toward both the broody and the chicks. Most adult flock members will be curious but maintain a safe distance from the broody, they may peck at the little ones if they get underfoot or don't wait their turn at the food dish. The flock will begin teaching them what that phrase 'pecking order' means from a young age. You have to determine the difference between normal pecking order 'corrections' and real aggression. If there are only one or two flock members who are aggressive then you may remove them to another area for a few days and then see how they do after the broody and chicks are more settled into the flock. If the broody freaks or just can't seem to handle the pressure from the flock then you may have to keep them separated by a hardware cloth fence for a bit longer. Keeping them in the same area but separated by a fence allows them to get used to each other but avoids direct conflicts.