Same for me on a PowerEdge 530 (Gen 13) with the 2.7.0 firmware, ESX 6.0 patched up to all the latest and greatest and Windows 2012R2 patched up and enabled to fix these issues. SpeculationControl tells me there's no hardware support for it.
Guess we can expect more patches incoming:
"VMware is working on Hypervisor-Assisted Guest Mitigation patches with the highest priority and they will be made available as soon as the testing process has concluded. This mitigation will include new patches for ESXi, and new versions of Workstation, Fusion, and vCenter Server."
(VMware Knowledge Base)