For a (large, critical) RHEL4 installation, we have need of the "--remove-sent-files" option which was introduced in rsync 2.6.4. Please consider updating the RHEL4 rsync to 2.6.4 or newer -- 2.6.6 is latest, and 2.6.5/.6 contain many other relevant bug fixes and efficiency enhancements -- for U3. The Dag packages are currently based on rsync 2.6.6 and appear to work fine in our testing (it's what we're running while waiting for official packages from RH).
There is a bug in versions < 2.6.4 related to compression (-z) and transfers of large files (>4GB). Rsyncing directories with large files may randomly fail, based on the actual file 'contents'. see: https://bugzilla.samba.org/show_bug.cgi?id=2187 I can repeatable produce the error mentioned in bugzilla report on current RedHat AS4. v. 2.6.4 is available in the Fedora Core4 release, but has not made it way into AS4 distribution. Considering the degree rsync is widely relied upon, and assumed to be bug free... I would urgently suggest pushing a new version on into RedHat Updates.
We usually don't do version upgrades in RHEL. If you need a new feature, contact your support person to open a bug to ask for this specific feature backported.