Although they never featured prominently in Deep Space 9 the Son’a from Insurrection were heavily implied to be associated with the Dominion.
I’ve set them up as fast ships with movement based abilities (in the movie they outran the Enterprise).
For captains we have the obvious Ru’afo and one of the minor characters (the name comes from one of the star trek card games). There’s also a crew upgrade to screw with enemy captains and crew. The star I think though is the subspace weapon which piles aux tokens on every ship within range 3 of the target.
Running out of Dominion War stuff now but there’s still a few little gems left. Gul Dukat’s independant faction B’Rel springs to mind…perhaps some more stations for scenario games and things like that.