I was just thinking, there are a few similarities. Both are unable to destroy the world. Sauron because he is pretty much nothing and Zeromous because he's stuck on the Moon. Sauron has the Wraiths and Saromon trying to get the One Ring, while Zeromous has Golbez collecting the Crystals. Both are pretty the tangible form of ultimate evil, comprised of hatered. This is all I could think of off the top of my head. Tell me if I missed anything.