[steve]

not really, Gollum is a living creature, or I should say was, the Nazgul are undead, soulless, beings under the controll of the One Ring, it was the One Ring that corrputed Smeagol, the Nazgul were not corrputed by the One Ring, they were corrputed by Sauron and their rings, not directly by the One ring like Smeagol was, and also, if they were to go insaine by the ring, sauron would just take controll of them again, or destroy them, and if sauron had the rings, would he not use them to his advantage?