People often say the Son'a are double crossing the Federation by being allies of the Dominion... but what if it's the other way around? What if the chance to survive/get revenge against the Bak'u outweighs their allegience to the Dominion so much that they're actually willing to double cross them and side with the Federation instead? All for the chance to get legal access to the Bak'u planet?
Well, they were enslaving other races, produced Ketracel White for the Dominion, and were ready to harm and kill the Ba'ku for the radiation, and eventually ready to kill Starfleet personel. They were gansters and opportunists. I had the impression they would sell the radiation simply to the highest bidder.