After spending hours and hours and then a lot more hours floating around this topic it was rather embarrassing to find that this was what I required to fix my problem:
Code:
apt-get -y install cron
crontab -u zimbra /tmp/crontab.zimbra
Of course I followed some other steps too such as those in post #10, but without having crontab installed I saw no results, only that annoying warning in zmstat.out and so on every minute or so which I guess is why I assume crontabs were working.
I don't know how I missed something so simple! Hope this helps relieve someone else of their grief.