Jim82 never mind, I solved the problem.
By changing a setting in the BIOS to tell the machine to wake on lan from the PCI device, I can wake the machine from a powerdown setting remotely using a utility downloaded from matcode.com.
I can use the vsphere client to power down the machine, and then use the utility to power it back on. This isn't as elegant as a solution as if the ESXi server would simply hibernate on its own, but a solution nontheless.
Matt