This I guess would depend on whether the original occupation force needed to be of significant military strength. In many cases, I could see a planet being kept subjugated by relatively weak forces that would never have been withdrawn from the world even during the height of the war. Although it could be argued that whenever the Alpha Axis powers observed such a world, they would have sent a small military unit of their own to help liberate the world, at very low cost to themselves but high cost to the Union...
Chiefly, though, I could see the campaign being waged much like the WWII Pacific one, with individual "islands" being denied strategic significance by controlling the shipping to and fro. This would reduce the value of fortresses, bases or raw material sources alike. In contrast, an actual attempt to conquer such a world might involve a high cost in lives, as there was some emphasis on bloody infantry-style warfare in the dialogue describing the Dominion War (even if we saw little of it on screen). In order to avoid the loss of life, the Alpha Axis might skip conquest, thus leaving the local infrastructure standing as well, and allowing the Union to resume exploitation operations unless the peace treaty specifically forbade them from doing so.
Of course, the UFP would be likely to insist on such a peace treaty on humanitarian grounds, even if the other Alpha partners would not. But the Feds might also decide to allow the Union to continue exploitation for humanitarian purposes (that is, to prevent mass starvation on Cardassia) if they just agreed to doing it more gently from now on.