Well, as far as I'm aware, Saddam Hussein was not in power when Dune was written. Saddam is not an uncommon name, and Shaddam may well be an real-life extant regional variation. Herbert has acknowledged that there is an intentional parallel between water and oil. Arrakis... I presume the word Rakis means damp or similar in Arabic or another language: Arrakis was dry,then became wet Rakis, then dry Arrakis. The a- idea is presumably from the greek privative alpha.