From speaking with VMware engineers, statistics gathering can only achieve by using VMware’s application programming interface (API).
That's not quite accurate. We do gather statistics via SNMP. What is also true is that there are statistics that are only available via Virtual Center using VMware's proprietary APIs. We don't have a way to do that yet. We've been talking with VMware about support more standard methods of data access. That may yet happen, or we may create a VMware-specific method for collecting data.