A number of deportees/refugees and passengers of this ilk show up at the aircraft door accompanied by a customs agent and with proper and approved documentation that clears the person involved for transportation on the flight. These papers (which usually include the travellers passport) are held by the flight crew until debarkation at the arrival destination. Sometimes at the arrival end the traveller is greeted by a customs, police of other authoritive officer. I hand the papers over to them and they escort the person off. If no one is specifically waiting for the person, I hand the pouch to the greet agent at the door.
Inadmissable people are a whole different breed and do not make it down the bridge to board the flight to my knowledge as they are already flagged in the computer system as such and are denied at the time they attempt to reserve or purchase a ticket. Hope this helps.