"For example, the long vent on wintercomplex. Once you stick a vender in there, no zombie can pull it out."
Once you shoot it all the way down, they can't get it out.
Another example is the vent in holdout moutain. It is hard to get in though, so if you happen to get a chance to do it, then you're one lucky guy.
"The exception to this rule is the crawlspace on snoopie, which cannot be caded at all."
Stick 3-4 people in there and you'll never get them period if they know what they're doing. If you're in there by yourself, then I can see why you would. Besides, deforms can still kill them.
"Even still, there are spots that are not crawlspaces that are cadeable such as the glass houses on beachstrike. If caded properly, and nobody throws any careless nades, it is impossible to break."
If you cade rooms properly, and know what your doing, then yeah, you should be able to live. Most the time I just kill those rooms by tagging people through the fences. There really isn't all that many places in Beachstrike for 40 people though. Most of the rooms your talking about aren't unbreakable, it's just highly improbably that you can. Remember that one time in Office? You said "That room is impossible to get into with the big vending machine!" Two seconds later I killed the two in there.
I have to ask though.. Why do I even care? I don't cade vents, unless its under the stairs in beachstrike, because there's so few places you can go. And you can't really hold off two sides with 2 people, unless they have shotguns. Even then, they can get trained.