We can put this one to bed. I have successfully upgraded to 4.5.10
To answer your question, I had only attempted one upgrade from 4.5.6 to 4.5.10, which finished with a successful completion message and no obvious errors in the logs. Running "zmprov gaa" showed no accounts except the spam and wiki users, no admin, no other users.
To resolve the problem, I used the "Exporting and Importing Zimbra LDAP Data" Power Tip to dump the 4.5.6 LDAP data before upgrading to 4.5.10.
After running the upgrade and following the Power Tip to restore the LDAP data, running "zmprov gaa" showed all accounts restored and were able to be logged into.
Thanks for all the help