The ecj sub-package (eclipse-ecj) has unversioned Obsoletes and Provides on "ecj". This limits options if someone needs to use a standalone ecj package. We are considering re-introducing a standalone ecj package in Fedora and having this in RHEL-5 would not allow upgrading cleanly from these packages to a future RHEL which may inherit the standalone ecj package.
RHEL 5 has ended Production Phase 1 and thus only security bugfixes from this point on. Please use Eclipse from RHEL 6 if you need newer Eclipse version.