I don't see 3.0.5.53 under official IBM RPM versions:
IBM Fileset information for: rpm.rte - United States (http://www-01.ibm.com/support/docview.wss?uid=isg1fileset1404816868)
It would seem that /opt/freeware/bin/rpm is linked with a version of the shared library /opt/freeware/lib/librpmbuild.so that is incompatible with the version of the statically linked /usr/lib/libc.a...