Anyone who dies in the Seretei becomes a part of Bach. Their talent, skills, and powers. This is because he touched the entire city with his powers, so anyone who dies be them a hollow, quincy, shinigame, or fullbringer is fair game for his majesty.
And about Ulquiorra. He is my favorite espada, but in the end he began to understand the heart and it's capability for compassion. Hardly the best villain as he just isn't evil, while Bach has to have war in order to absorb souls and live forever.