That's if it works the way that we assume it works. NVidia didn't do it the way that one would think, just sending you out a code that you redeem on xbox.com. They redeemed it themselves. Now how that is setup can make it very hard or easy for NVidia. 
They can have a 1:1 match from their code to a ms code in the database.
Or
They could have a code that just gives you access to take whatever key is at the top of a list without associating them and redeem it on your behalf. Funny enough, the reason why they asked to do stuff on your behalf is to make it easier and so that you can't see the code that they used to protect against piracy.
But yes, I agree, that's a lot of hoops to go through.