First check this to see how you enable a host to be checked with nagios over SSH.

Create a command in /etc/nagios3/commands.cfg:

# This command needs this in /etc/sudoers on the target:
# nagios ALL = NOPASSWD: /usr/local/sbin/
define command {
       command_name     check_3ware
       command_line     /usr/lib/nagios/plugins/check_by_ssh -H $HOSTADDRESS$ -i /etc/nagios3/id_rsa -l nagios -t 25 -C 'sudo'

Run visudo and add this line:

nagios ALL = NOPASSWD: /usr/local/sbin/

Then install the script from here. Last time I did that I needed to fix bugs in it, so beware. I submitted a patch, which will be accepted I guess.

Then go download the tw_cli tool.

Then create a hostgroup for your 3ware hosts:

define hostgroup {
        hostgroup_name  3ware-machines
        alias           3Ware machines
        members         boxen

Then a service:

define service {
        hostgroup_name                  3ware-machines
        service_description             3Ware status
        check_command                   check_3ware
        use                             generic-service
        notification_interval           0

That should be it.