We have a small splunk server up and running. More a proof of concept, but we believe its the right solution for our future.
At the moment we bought the vmware app., so we can work with the data.
The performance metrics of the esx server is aggregated from the vcenter and not the detailed metrics from the host itself. So if we would find problems or peaks, its not possible at the moment. I think the ITSI app would show us more detailed informations, but the price is to heavy. We only need 10% of the itsi solution.
I would be happy to discuss what possible alternatives there might be and that would depend on what you are looking to achieve in the end. What are you using today if anything besides what vmware might offer you in vCenter? Are you looking for perfromance metrics of the hosts and guests, along with logs or a narrower scope? Are you a current Splunk customer and if so, what does your deployment consist of today?