I would not keep him in a crate for a month? I wonder if you miss understood that direction. Usually they are kept separate for a month for quarantine, however if it is in the coop, that is not quarantine.
I would not attempt this, if you want multiple roosters to work together in a flock, IMO a cockerel raised up in the flock, so that there is a father/son relationship, so to speak, tends to work a wee bit better than most other situations.
Brothers or brother relationships sometimes work, sometimes work for a while, and sometimes never work.
Introducing a strange rooster to an established flock is asking for a cock-fight. How violent depends on the amount of space you have, the hormone level of the birds, and a lot of luck. This needs to be your main worry. Roosters and hens generally figure it out. As Ridgerunner says, it might work, but I would want a way to get a hold of each rooster to separate it AT HAND.
Good luck,
Mrs K