Granted this is the thing I've looked at least but my system team tell me that we are not see any usable details with our ESX Monitoring. Only one node is showing a virtual machine (only 1 windows file server) and all 15 others are showing nothing at all. Credentials validate OK. Am I missing anything obvious?
Can you open a support ticket to investigate. If you are using the API only, you should see the list of guests on that ESX along with stacked charts regarding guest usage of CPU, Memory and Traffic. If you have also enabled SNMP, you should also see CPU/Memory of the ESX as well as volumes and interface details.
Take a look at the online demo at one of our ESX boxes and this is the type of data you should be seeing.