Another tactic would be Jemhadar beaming aboard borg ships with exploisves. They would be cloaked they would reach vital parts then blow themselfs up. If the Dominions smart they will have dead man switched so if the borg detect them and try and assimilate them BANG!
Rember the Jemhadar would sacrifice themself at the drop of a hat. And there is no way they would allow themselfs to be assimilated. They would get limited returns via assimilation.
For every 100,000 borg killed they would get only a handfull of drones.