I've also always played the Outcasts as Italian, but I guess it boils down to preference. Nowhere does it really state one way or the other.
As for the Italian in Assassin's Creed...I first played it Italian, and it's fantastic, really, some of the best voice acting I've ever seen. Then I played it in English. Ah, the horror..:no:
Edit: some short videos for comparison. Granted that these are not the best scenes either way. they are the only ones I could find both in English and Italian xD.
Edit n2: now that I remember, the worst part is not the "Italian accent" they try to fake. It's when they actually try to say stuff in Italian, like names. Ezio Auditore da Firenze is the worst of all :|