Certainly Guetta is a real person who has been in LA making his own art under the MBW name for years. This is reasonably well-known, as the article you link to notes.
What's harder to tell is (1) to what degree Banksy and Shepard Fairey are behind the making of the MBW art work, and (2) to what degree the movie was shot by MBW and just arranged by Banksy as was claimed in the movie.
About (1), of course Guetta does not do all the MBW work. Lots of artists use fabricators; this is even shown in the movie. So in order to answer (1), all the sudden you're down in the details of which particular pieces Guetta did do, what percentage, whatever. Booo-ring.
You can ask very well-informed people who have followed the LA art scene for years (relatives hounded my wife to ask her friend, the editor of http://coagula.com/) and they can't fully answer these questions. Also, they don't want spend energy to find the answer, because the uncertainty is part of the point.
"Outsiders" seem to really want to know, however, perhaps because it will make them "insiders" in their own minds.
The movie definitely grows in value when you realize there's a huge real-life prank going on, and that no-one is quite sure exactly what it is. Kind of like not being sure if you're on a seedy street or in an art gallery. But that's a big part of the feeling that street art is supposed to give you, as nearly as I can tell, and Banksy and Fairey are at the top of the game at it.
For me, one of the big mysteries is who actually made the movie. You mean to tell me that Banksy and Shepard Fairey made that? It's a very well-done movie. It sets off new and old footage really well. It's engaging and provocative. So they do street art very well, and are really good at making films? Seems to much to hope for, but it certainly could be true. That's part of the fun, I think. :-)
Of course that would defeat the purpose of the original. But people would come to associate the forms (spraypaint stencil, physical pranks, etc) with the corporate message, and then anyone who saw the originals would think of the corporate message instead of the subversive one.
The movie invents a character who represents those commercial interests. Mr. Brainwash tries to cash in on the popularity of the art by copying the forms without the meaning. By the end of the movie he is a laughingstock - and the audience has been trained to avoid capitalistic dreck in the form of art. Banksy mentally inoculated the audience against exploitation!
Pop music is the best example this, but shockingly it was pro wrestling that blazed the trail.