How far apart are you going to be able to keep him? The truth is, if you don't do quarantine exactly right, you may as well save yourself the work, and not do it at all. Now I am not advocating just putting any bird in with your flock. But a flock of birds, that are relatively close to you, that probably have not been exposed to strange birds (ask) say from an auction or a fair, probably have been raised in a very similar environment as your own birds. If those birds look healthy, they probably are. Diseases mostly come from exposure to sick birds, over crowding, and poor sanitation.
Proper quarantine is generally impossible in a backyard set up, I think it is 300 feet separation, complete change of clothing and shoes between sets of birds, different watering and feeding bowls. Most people just cannot do that. If you don't do this, well you are just pretending to quarantine, and your flock is at risk. My point is while it is a risk, it is not a real big risk. If you have a valuable flock, if you would be devastated to lose this flock, then maybe not. But if this is a hobby, and you really want the roos, and you are not set up to quarantine well then...I would just put him in with your birds. Adding a rooster is one of the easiest integrations.