I've been working on using Nagios more for availability monitoring but it is severely disjointed in Alienvault USM and OSSIM. If you want to use Nagios for anything more than up/down monitoring of hosts and ports you need to Jailbreak the SIEM and manually edit the confs. Would like to see the ability to enable other Nagios plugins and be able to edit the nagios confs from the web interface. It would also be helpful to include additional base nagios checks such as check_wmi_plus and check_nwc_health. These plugins would cover monitoring services and hardware for windows and most networking equip.
To work around this issue until an office fix, I built a NagiosQL instance on another server that allows me to enable custom checks and manage the confs more efficiently. It pushes the confs over SSH and the only downside is that Nagios service needs to be restarted each time a conf is changed. I suspect you could leverage this method from the web interface and automate the restart of nagios through Ansible.