No, the writers simply collaborated well as they went along. Indeed, the Dominion War was supposed to be a smaller affair, wrapped up in 2-3 episodes at the beginning of season 5 (I believe), but other things got in the way. First, introducing Worf and the Klingon conflict pushed the war back. Second, the writers, individually, wanted to accomplish more with their individual episodes, requiring more and more time (luckily, they kept talking with one another, so that the next episode was influenced by what happened previously). Third, the Dominon War became the framework within which all the other narratives were explored: the Emissary, the Cardassians, the Klingons, etc. With the increasingly complexity of the Dominion War, it couldn't be wrapped up as quickly as anticipated, eventually consuming the rest of the series. If you want details, you should find the DS9 Companion.