Jan used the zoo to their advantage and had he not they probably would have been a casualty. He convinces Heck to let him use the zoo as a pig farm to feed German soldiers. Jan, he was a master planner and a good manipulator. He even found a way to poison some of the German soldiers during that time. Later the zoo proved useful as a fur farm.
The Zabinski's used these situations to their advantage. They hid people in plain sight