I would consider the risks and quarantine needed for a shelter bird to be pretty much the same as one from a sale or swap.
We thought about adopting what was listed as a rooster, although it looked like a cockerel to me, at one point. This was from the big county humane shelter, not a rescue and they wanted to come do a home inspection. This shelter doesn't even require that for dogs. There's nothing on their web site about home inspections and I wonder if it was the idea of the only person there that handles the chickens. She said we had to wait until the next week to be able to see him, because she was the only person at the shelter allowed to show the chickens to you. Then she said we'd need a home inspection, in addition to the application and vet references. By the time she came back to work, I had the flu, so we just passed on it. I was just too sick to want that much of a hassle.