Now the data import works (appears to work). You have indeed to sync half a dozen passwords by hand before you are able to successfully restore you data.
Not to mention manually resetting the database with the peculiarity under Mac OS X with more than 5GB RAM (you have to issue "/opt/local/libexex/zmmyinit --mysql_memory_percent 10" or something).
Still the documentation could be somewhat more precise here, as normally whan you need a desaster recovery you need it ASAP. I will see whether I can contribute something in this regard in the Wiki.
While the Admin manual coming with the Zimbra download only lacks some minor bit of explanation regarding the LDAP password sync, the online docs:
Backup and Restore are missing the part of password sync entirely.