I have succesfully configured a Domino server (R9) to play nice with SNMP.
And I have configured a Nagios server to query status on numerous parameters on the Domino server.
Here is a screen dump from my Nagios Service status page
The blue ones are Domino specific.
The two red ones are the ones I am glad to have working. At the moment there are 0 mails pending og the availability index is 99. Which is good.
I got it working by dusting off my German skills and reading this blog entry; Monitoring von IBM Domino-Servern mit Nagios.
The blog was not a perfect fit for my needs. The author includes instructions on doing some deep probing of the Domino server that I did not need, like how many documents are found in a specific View in a certain Notes Database - using DIIOP. So I had to disable some of the Service examples that are in the download package. Also, there are some minor errors in the samples.
You do need to download the example package to understand how things are done.
I wrote some more on Nagios a while back: Nerd alert: Home server with Nagios, Pushover and Blink(1) warnings.