The use of stock footage and recreations is common practice in all avenues of filmmaking, including documentaries. Whether the footage comes from a hollywood production or a film library isn't a concern.
What's more, the footage is used to illustrate a non-controversial point, namely that the poles of the planet are spectacular.
The use of pre-existing footage probably saved the production tens of thousands of dollars. Putting a camera plane over the arctic can't be cheap. And why cgi? Well, you could rent that plane for days on end, trying to find the right shot, and still come away with something you weren't completely happy with...or you could make the shot digitally, saving money and getting the visual you want.
The only inconvenient truth in this thread is that filmmakers too must bow to the constraints of economics.