This is an odd question..
What exactly are the risks of power failure/hard shutdown/hot backup/etc in zimbra?
What services don't work right, and how complicated is recovery?
I'm wondering about using LVM snapshots, but without shutting down the server for the daily backups, and once a week/month do a "full" by doing a shutdown, lvm snapshot, startup.
I also pondered the idea of a standby server, using lsyncd but this would depend on how tolerant a slightly inconsistent state is and how easily that can be recovered.
If all you are going to say is "Bad idea, don't do it" save yourself the time to type; as I've already thought that initially to myself. Hence the "weekly fulls".