Millar tends to write his comics in the wide-screen style - like picture-boards for a movie. So having him as a consultant for movies is actually a fairly good fit for his abilities. He has an exciting style for big moments and action scenes.
That being said, he will need to tone down his adult content considerably. I've also been critical of his grasp of Marvel's character's personalities and histories (Civil War had nearly every character being portrayed out-of-character, in my opinion).
Millar was the guy who cut his teeth on the DC Animated Universe stuff (winning an Eisner for his Superman work). His Ultimate FF and Ultimate X-Men weren't all that illicit. Even his Ultimates (barring the Hank Pym/Wasp Domestic Violence and Hulk Rapes and Eats People) wasn't that explicit and could easily be edited out.
And he is just going to be a consultant. He isn't going to be the writer. If anything, he's going to be the guy who says, "This property would be great as a Paul Thomas Anderson movie. Or this one would be perfect for a Michael Bay style movie.