This is just a direct link to the HP Blog article itself but worth a read if you are looking at monitoring any HP server running ESX or ESXi. The main bit that I have always found is that you need to install the HP extensions for ESXi installed as this greatly improves what you can see from remote tools such as Insight Remote Support, Nagios/Opsview or from the vSphere client itself.
The link to the article can be found here – http://h30507.www3.hp.com/t5/Technical-Support-Services-Blog/6-Simple-Steps-to-Monitoring-ESXi-with-Insight-Remote-Support/ba-p/100789