Wasn't that pretty much what they were doing with the Evora in Insurrection and what Bajor was during DS9's TV run?
Pretty much. At least as far as Bajor goes, it remained a sovereign world, capable of terminating its relationship with the UFP at any point, but the Federation was committed to defending Bajor. But in no way did the Federation claim Bajor as its own territory, nor was there ever any indication of Bajor having a "non-voting member" on the Federation Council (unlike Puerto Rico's relationship with the U.S., where P.R. is U.S. territory, but it doesn't have say real voice in Congress or presidential elections, just a non-voting Resident Commissioner). (Well, until Bajor was formally accepted as a Federation Member, of course.) Presumably, the same is true of the Evora.