There will likely be side swipes biting as they pass eachother. There may be chasing: I stay with the chase as that can end with one drake standing on the other to exert dominance. Standing is OK in my book as dominance demonstrated generally reduces pecking order behavior. But when one drake...
If he and the jumbo pekin are sitting each side of a barrier, I would be tempted to try the two together with close supervision initially. If there is no serious pecking order behavior, your jumbo will be a good ally to stop aggression from the others. If that doesn't work out, then go to your...
Good plan! Yes, drakes often have pecking order in access to their pool and food. That looks like one at a time, if enforced down the order. My boss drake enforces his status but the other boys generally do not. So after boss drake's first dibs, the others are more likely to share.
I agree with @Miss Lydia
As you have a setup thst works so that the new, healing, drake is not lonely, keep doing the same until the fall when the new one will have fully healed and, with extra niacin and vitamins should have his energy levels back. You could give him Rooster Booster Poultry...