I always thought given his Arabic Name, the whole Assassin angle and the immortality that Ra's was implied to be the old man of the mountain and the league to be the descendants of the historical assassins.There was the Ras/ Ducard amalgam and Ras not being Arabic as he was in the comics.
I don't recall Ra's being established in the comics as Arabic. What I recall is that his ethnicity was deliberately left ambiguous, that "Ra's al Ghul" was a title he adopted. True, I do seem to recall that Birth of the Demon showed him living in an Arab community when he became the man he is, but I think it was stated or at least hinted that he came from somewhere else.