There are two issues with the ucd-snmp-4.0.1-4 package that comes with Red Hat 6.1: 1. The -devel package is missing the /usr/include/ucd-snmp/scapi.h file, causing certain programs to fail compilation, e.g. the SNMP perl module. Other headers might also missing (keytools.h, lcd_time.h, readconfig.h, scapi.h, snmp-tc.h, snmp_alarm.h, snmp_debug.h, snmp_logging.h, snmpusm.h, snmpv3.h, tools.h, transform_oids.h, ucd-snmp-includes.h). This is a problem with snmplib/Makefile.in, since it fails to include these important files in the ALLHEADERS and INSTALLHEADERS definitions. 2. The %postun section uses chkconfig to delete the snmpd service after the init script has already been deleted. The chkconfig command needs to be moved to a %preun section. (/sbin/ldconfig should stay in %postun).
The problem 1) is fixed in ucd-snmp-4.1.1. I've built CPAN modules against that version. The problem 2) is fixed in ucd-snmp-4.1.1-2 from Raw Hide, thanks for noticing.