Other dependencies are (at least for RHEL 6.1):
- libstdc++.i686
- file.x86_64
- nc.x86_64
You will also need to use visudo to edit /etc/sudoers, and add the following after Defaults requiretty (or you will receive errors when Zimbra tries to start its LDAP server for the first time due to the zimbra user not having a TTY), so that it looks like this:
Code:
Defaults requiretty
Defaults:zimbra !requiretty
Defaults:%zimbra !requiretty
The first line is the RHEL default requiring TTY for all users, with the second and third lines exempting the zimbra user and group.
Other than the above, the installation guide should work fine 
Cheers,
Ali