I believe so. If a speech pattern can be analysed and identified, then I believe it can be copied and manipulated. Probably even digitally created, to match something with known parameters.
Impossible. You'd have to have recorded, identified and categorized every single word Saddam, all his aides and all his generals could possibly have uttered and in every single tone of voice they could possibly have uttered them in order to attempt such manipulation.
We're not talking a few guys in an al Jazeera studio, editing clips of old tapes together to send a new message from a dead guy, we're talking a LOT of people, interacting, arguing, debating, demanding explanations and data etc.