I saw this a long time ago, when I was looking for minigames, and now that I'm seeing it here, I'm wondering how it isnt featured yet, it is a great idea, but gets confusing at times, but anyways, =)
I have tried it with my friends, and it is possible for: A: the humans to get out and B: the zombie to climb up to the top. I was using the appropriate map and game type.