Troubles monitoring a zimbra installation with nagios

I am trying to monitor my legacy zimbra installation (running on an outdated Ubuntu 8.x) from my nagios install (running on a more recent OpenBSD).

The problem is that when I run check_nrpe from the nagios server it complains:

nagios-server$ sudo su -m _nagios -c "/usr/local/libexec/nagios/check_nrpe -H ZIMBRA_HOST -c check_zimbra"
CHECK_NRPE: No output returned from daemon.

Note that the zimbra server’s NRPE configuration runs:

command[check_zimbra]=/usr/lib/nagios/plugins/check_zimbra.pl

On the other hand, running the plugin locally on the zimbra server works fine from root:

zimbra-server# ./check_zimbra.pl 
HOST : ZIMBRA_HOST, ldap : OK, logger : STOPPED and zmlogswatchctl down, mailbox : OK, mta : STOPPED and zmmtaconfigctl down and zmsaslauthdctl down, snmp : STOPPED, spell : OK, stats : OK

However, running it as nagios user on the zimbra server complains about the path:

zimbra-server# su -m nagios -c "./check_zimbra.pl" 
Insecure $ENV{PATH} while running setuid at ./check_zimbra.pl line 32.

Line 32 recites:

7  $zimbra_status_command='/opt/zimbra/bin/zmcontrol status';
[snip]
32 open (ZMSTATUS, "$zimbra_status_command |");

I have a suspicion it might have something to do with suid perl. In fact, following this advice and adding this line to the check_zimbra.pl file,

delete @ENV{'PATH', 'IFS', 'CDPATH', 'ENV', 'BASH_ENV'};

I get the following:

zimbra-server# su -m nagios -c "./check_zimbra.pl" 
Insecure dependency in piped open while running setuid at /opt/zimbra/bin/zmcontrol line 389.

Anyhow, on the zimbra server I have installed the check_zimbra.pl plugin, which is suid zimbra so I can run it from the nagios user:

zimbra-server# ls -la check_zimbra.pl 
-rwsr-xr-x 1 zimbra root 2885 2010-01-11 21:14 check_zimbra.pl

I have modified /etc/sudoers so that the nagios user can run the appropriate zimbra monitoring tool:

%nagios ALL=(zimbra) NOPASSWD:/opt/zimbra/bin/zmcontrol

I am stuck.. is there any other way to run the check_zimbra.pl plugin as nagios user, being able to run the zmcontrol status command as zimbra user..?

Thanks,