And that baldness was unintentional. The Nemesis script describes Shinzon as having "long flowing blond hair." But Tom Hardy had to shave his head for another movie he finished filming not long before Nemesis began and since he didn't have time to grow long flowing hair or dye it blond, they decided to keep him bald.
The movie didn't seem to know how to address the similarity of lack thereof between Patrick Stewart and Tom Hardy. Picard and Shinzon's early conversation in the Romulan Senate Shinzon explains why he looks so different than Picard did at a younger age with thing like a broken jaw and whatever from hardships of life as a slave in a mining camp, but then later in the movie Picard pulls out a picture of himself as a cadet looking exactly like Shinzon.