The search returned the working address.
I received an email notification today from the firstname.lastname@example.org address. However, going back into the Admin interface -> Accounts still does not show the account available. I double-checked for sanity sake
zimbra@zimbra:~$ ldapsearch -x -h zimbra.domain.com | grep nod
# nod32, people, domain.com
I'm also able to log into the web client as email@example.com properly.
So the account is there, and working. But the admin GUI does not show it listed for editing/management.