I have centos 6.3 machine and did a yum install monit (version monit 5.1.1-4.el6 from epel) and then I setup the up the http://mmonit.com/wiki/Monit/Upstart and tried to start monit initctl start monit initctl: Job failed to start. I did on another machine I download the .rpm file of monit-5.3.2-2.el6.rf.x86_64.rpm and did the the same and able to start via initctl method. What could be missing in the epel version ?
They're entirely different versions. The official Monit release is at version 5.5 right now.
Use the newer Monit available from RPMForge/RepoForge. The old one available via EPEL doesn't support the feature you wish to use.