The machine what you tried to monitor should be the vCenter machine.
But in your case it looks like you already have data for this machine. The ESX Memory/Snapshot checks are showing some results. From does this data comes? I think your vCenter should run in the same environment. Do you also monitor the ESX servers by itself with the special agent? With actual 1.6 CMK you only need to monitor the ESX machines or the vCenter with the special agent. Booth are not needed.