In version 6.5 Veeam ONE is using CIM-XML over MOB to monitor hardware status.
Prior to v6.5, some hardware sensors did not return the correct status due to a known VMware issue - when host's sensors display wrong status via vCenter Server's Managed Objects Browser (MOB). In v6.5 a more accurate hardware monitoring protocol CIM-XML is used, which completely eliminates such behavior. Be aware that vSphere Client uses the same protocol to obtain sensors' states.
Moreover, starting with Veeam ONE v6.5 the hardware monitoring became more granular, and you may notice way more sensors available in v6.5 compared to v6.0. But for some sensors, VMware does not have any state and returns the 'unknown' status. Please keep in mind that the correct state for 'well-known sensors' is always available via CIM-XML (which is utilized by Veeam ONE by default).