Hi!
I like this one, because it's a thing which bother me since years.
I my opinion, zope is not rock solid. It's a really nice software, but you can not rely on it. If something go wrong deep inside, you may have all your zsever threads blocked. Then you will need some external software to check if the web server still reply, if not you will have to kill and restart it. I don't think ZDaemon (-Z arg?) is of any help in case of hang.
Of course you CAN make Zope unstable. But you can also write unstable modules for Apache I guess. We have never experienced any of these hangs. There was a single Zope Beta I can remember that collapsed every few hours. But the latest releases were all stable in the core. Having Apache run in front of Zope is a very good idea though. Just do be on the safe end with regard to malformed requests and denial of service attacks. Joachim