I didn't want to entirely disable the TTY requirement, but the 'ldap' exclusion given above didn't work for me. After figuring out what sudoers is all about (thanks to the link to the docs), I came up with this solution:
Code:
Defaults requiretty
Defaults:%zimbra !requiretty
Defaults:zimbra !requiretty
The first line requires TTY for everyone not excluded by the following lines.
The second line exempts the 'zimbra' group from the requirement.
The third line specifically exempts the 'zimbra' user (the account listed as attempting to install the service according to the logs). This may be redundant, but it worked for me.
I did not exempt the 'ldap' user as shown above, and it, apparently, is not necessary to do so to install and run Zimbra.
I installed this on Scientific Linux 5.3 i386 32-bit, so it should also work on RHEL 5 and CentOS 5. (No guarantees, of course)
