How does the GDID compare to the UDID (Unique Device Identifier) and serial number in iOS; and the Apple Hardware UUID and serial number of Macs?

well, mostly the name. And the fact MS gave away GDID - IP mapping to the govt.

	▲	autoexec 2 hours ago \| parent [-]
		Is there any reason to think that the government couldn't force Apple to hand over the same data? They may or may not have taken over entire rooms at Apple (https://en.wikipedia.org/wiki/Room_641A) but you can bet they've at least got devices sitting on their network collecting data.