Cardscan is quite good at creating contacts by scanning business cards. It can export the contacts into an Outlook personal folder (i didn't try exporting directly into a shared folder - too scary for me). Copying the contacts from a personal folder into a zimbra shared folder worked fine, but the contacts would not sync to the server.

After a few hours I discovered that the message type of the contacts from cardscan were IPM.Contact.Something while the contacts that synced ok were simply IPM.Contact. I found this tool that will convert the message type.

ContactGenie - Message Class Modifier for MS Outlook '2000-'2007

Once the message type is converted in the personal folder (prior to copying into a share folder), then the syncing worked.

So the sequence is:
- export contacts from cardscan into outlook personal folder
- use the CG-MCM tool above to convert the message type of the contacts to IPM.Contact
- copy or move the contacts to the desired shared zimbra folder

Hope this saves someone some time...