I installed ITSI and the vmware addon. The vmware addon already import alot of data from vcenters/hosts to splunk.
With these search: index=vmware* tag=virtualization I see over 130k events.
I created in ITSI a service which uses the prebuilts KPIs of virtualization,hypervisor,datastore. I didnt change any setting. My KPIs tells me that there is no data.