Okay, it seems as if the rule for your ESX-host is taking effect, but something seems wrong with the credentials. Can you try to log in to the webinterface of the ESX-host with the credentials you provided in the rule? Can you specify other known working credentials (e.g. for the root-user) in the rule and see if that works? Are you trying to contact a standalone ESX-host or a vCenter?
Piggyback information is always useful and you also get some information there you won’t get with the agent, but i would always consider the agent installed on the target system as the most important source for monitoring a host.