During Chapter 2, the only zombie you are allowed to kill to get the "À La Corvo" trophy is the very first one where you obtain the revolver. You may damage other zombies, but do not kill them with your weapons or melee attacks. However, it is fine if they walk into traps and kill themselves. This does not count as a kill and will not void the trophy. Just run past all enemies. It does not matter if they see you or not. When you reach the gate, you have to open it with a crank. Some zombies will wake up nearby and attack you. When this happens, let go of the crank and lure them far away. Then, run back to the gate and open it.