So you have a planet that's within Federation space but not a member of the Federation. You have a race which isn't part of the Federation but want's to travel to that planet, would it not be polite to ask the Federation permission to traverse their space? The Federation of course would ask why to you want to go there, and perhaps Federation invovlment started there.
sure, but if the Son'a tell them the truth, then the Federation's going to decide that it's a PD issue, and an internal conflict between the Son'a and the Baku.(Picard HIMSELF calls it a "blood feud.") There response SHOULD BE "do whatever you want, not our problem, we'll be happy to keep this secret between us and we'll buy your particles that you get from this."
So either the Son'a are incredibly stupid for not just telling the Federation the truth, OR WE'RE MEANT TO THINK IT'S REGARDED AS A FEDERATION PLANET. Otherwise, the Son'a-UFP partnership makes no sense.
Again, the movie's premise is just unsalvageable. At least it is when you throw in the Son'a-Baku relationship. The Baku, as written, are a doomed society either way UNLESS the Federation is willing to just permanently defend them in violation of the PD for no real reason, while getting NOTHING from the Baku.