Hi Dan, and welcome to the VMware Communities!
The good news is that we are working on this and have made good progress. It's not quite polished, but the infrastructure is now in place. If you are feeling adventurous want to try it out, grab the VMware Fusion Tech Preview 2013, and add the following config option to the VM's .vmx file:
SMBIOS.reflectHost = "TRUE"
With that option, the virtual machine will use the same hardware model information as the host (i.e. System Profiler inside the guest will report the same model information as the host). Since the model information is embedded into the Time Machine backups and is checked at restore time, this won't necessarily help with full system restores from existing backup sets, but it should allow newly-created backup sets to be restored successfully.
Note that the Tech Preview is pre-release software, so it's not for everyone... Make sure you have adequate backups of your virtual machines (i.e. a full copy of the VMs taken while they are powered off) if you choose to play with the Tech Preview.
Cheers,
--
Darius