What are the hardware requirements for Hypervisor.framework?
Apple's documentation for the Hypervisor framework (https://developer.apple.com/library/mac/documentation/DriversKernelHardware/Reference/Hypervisor/index.html) mentions that the processor needs to support Unrestricted Mode, which is a feature available only on a Westmere or newer generation Intel processor. Seeing as the Westmere generation was released on January of 2010, your Mac Pro most likely doesn't support this.