It's related more to his own binary nature and his relationship to Sotha Sil and Almalexia. He's a hermaphrodite, he's bipolar, and he exists simultaneously in multiple universes. He is the "warrior poet", who has mastered both grace and violence. He's sort of the middle-ground between Almalexia (feminine) and Sotha Sil (masculine), as he embodies both feminine and masculine traits. It's implied in the 36 lessons that Sotha Sil and Almalexia could not have become gods without Vivec, the joining element.
That's an extremely abridged explanation, but I think you get the idea. Vivec is probably the most realised character in videogame fiction. Michael Kirkbride became obsessed with him, and wrote at least a novel's worth of information regarding his life. In fact, he still occasionally produces new tidbits of (usually very obscure) lore related to Morrowind and Vivec.