From rules perspective it is a theme list from the Abyssal Dwarfs, meaning you cannot ally in Abyssal Dwarfs with the theme, but oddly you can ally in their free bretherin the Ratkin, from a fluff perspective that is quite jarring, esp as the Ratkin tore apart their Abyssal Dwarven masters during The Great Revolt.
I chose to play Ratkin Slaves, at it seemed no other bugger was, and I wanted to find out if there was a “winning list”.