A deleted scene in INS which involved Riker and Troi in the library; Riker says something to the extent that the Son'a came to the Federation for assistance because the planet is in Fed space. So legally the Federation would have jurisdiction over the planet. This could explain the collaborate agreement between the Admiral Doughtery and Ru'afo. The Son'a filed all the legal paperwork and went through the proper channels seeking Federation help. The Federation would've gained technology and the methods to replicate the metaphasic particles of the planet for collaborating with the Son'a.
On the surface it seems legit. The Son'a however neglected to mention that the 600 occupants of the planet were their relatives.