nrpe and nsca are used to execute local checks on remote boxes… you need the nrpe daemon to be running and i don’t see much sense in using nrpe on the localhost…
to monitor nagios itself you may check with ps -ef if the nagios process is runnning or run “/etc/init.d/nagios status”… or better have two separate boxes check each other if the nagios process is running… this would then require nrpe or nsca… but not the single host to check itself.