It would be a possible way to hunt the Borg to extinction, yes. But why try such a thing if it doesn't result in your own survival, or even contribute to the survival of your friends and neighbors? Sacrificing one planet is fine for greater good, arguably. Sacrificing all of them means defeat.
Unless the idea is that the Borg would stop because they realize they aren't getting Drones this way. But why should they stop? They
aren't losing anything by making all these rigged planets go poof. That is, they wouldn't win anything by ceasing to make them go poof.
I guess it comes down to whether the Borg are serious about their two fundamental agendas: seeking perfection and spreading it to the masses through assimilation. The one and only reason not
to hit a species rigged for self-destruct would be because the Borg feel pity for the lost souls. But the Borg might feel that any folks left unassimilated and thus unsaved will contribute to imperfection, so it's a good idea to have them die of the self-destruct plague!