Wasn't there also supposed to be a return of the Vaadwaur in a future VOY episode?
As for DS9's Hunters, I believe the plan was that they and the Tosk are members of the Dominion. Notice how much the Tosk look like 'prototype' Jem'Hadar? They even have exactly the same 'shrouding' ability. Reportedly both the Tosk and the Jem'Hadar were created from the same 'original' race (the Hunters are the navigators/trackers of the Dominion, and the Tosk were basically given to them by the Founders as gifts).
A Hunter was even supposed to take the helm of the Defiant
(while piloting it to the Founders' homeworld) in "Broken Link" but for some reason this was changed to a Jem'Hadar at the last minute.