Wait I re-read that, you're saying you're not going to take a 2nd rsync with Zimbra shutdown; that really is just ripe for a multitude of issues - from PID's to database, index, and store changes. Yes you may get it up and running with slight finesse in a pinch, but I would still take that cold copy occasionally. By doing the 1st rsync you can minimize both your downtime (& risk) considerably.
Plenty of methods:
Backup and Restore Articles - Zimbra :: Wiki Open Source Edition Backup Procedure - Zimbra :: Wiki