The sendmail-devel headers and possibly the library are 5 years out of year date. They contain headers from 2006 while sendmail / libmilter 8.14 have headers from 2009. The structures and handling of SMFI_VERSION have changed between 8.13 and 8.14. This causes build problem, crashes, and failure for some milters to use newer features.
Red Hat Enterprise Linux 5 entered Production 2 phase. The focus for minor releases during this phase lies on resolving urgent or high priority bugs. For more details see https://access.redhat.com/support/policy/updates/errata/. As this bug is not qualified as urgent or high priority it is closed with resolution WONTFIX. This issue is already fixed in Red Hat Enterprise Linux 6. If this issue is critical for your business you can escalate it through the support channel (http://www.redhat.com/support/).