Actually a good point, I don't think it's called out directly in a single property. You'll probably have to get the VirtualMachineSnapshot object, and look at it's configuration at that point in time (config.hardware). Then find the disk (by key or file backing), look up it's controllerKey (to get the SCSI/IDE controller type).
You should probably pull out the controller type for each disk, maybe even get the SCSI bus ID as that might be of some impact depending on their infrastructure setup.