[falcolas]

I think you're looking at it backwards. Nagios shouldn't integrate with your inventory management; inventory management should be configuring Nagios. Chef, Puppet and Ansible all have modules for idempotently configuring services in Nagios, making it simple to have your nagios configuration be part of your inventory management solution.

Ideally, this also resolves your configuration management problem as well. If it does not, there are tools which can probe a running Nagios state file, and provide you feedback on what's being monitored, and its state. The python library nagparser is one that I've used in the past to probe Nagios status for a status aggregation tool.