Guess it depends on how dedicated he was to the project and his performance. Actors didn't get payed any extra money to dub their own lines so if they did it, they did so for the sake of their performance. Most of the old pros working abroad, such as Arthur Kennedy and Carroll Baker, almost always dubbed themselves. I'm sure they did it for the sake of their performance and because their voices were well-known to American audiences, who would notice if they were dubbed by others. But there are several examples of British or American actors working in Italian films who didn't bother to dub their own lines.