I mean in the recent film version of The Phantom of the Opera. We'll pass over its other defects (that it's Andrew Lloyd Webber, that Raoul is a huge sissy).
The name is spelled "Raoul." It is not pronounced "rowl" (to rhyme with "growl"), despite what Emmy Rossum appears to think. There are three whole vowels there, so a diphthong is not a possibility here. The sequence "aou" does not spell "ow."
These three vowels must be split. As I see it, you have two options. One is to split into "ao" and "u," thus giving you an "ow" (as in "I have bumped my elbow") and an "euw"--remember, this is French. This gives you "Row-euwl," which no man has ever named his son.
Your other, and the correct, option is to split it into the "a" and the "ou." This gives you "ah" and "oo," which are both known sounds in French and other languages. Further, you are left with "Rah-ool," which is a name I wouldn't mind giving my own son.
The parallel case of Raúl in Spanish is instructive, and as it bears an accent also completely unambiguous. Still, the case of "Raoul" is not so difficult, and film studios should really hire dialect coaches who aren't tin-eared imbeciles.