Your strategy seems to be the only one that would work against a zealer... but its not like it would be easy.. bone spirit is fairly easy to dodge especially w/ charge, although your mana would run out quickly. You see though your way would be like dueling against a bone necro, not a summoner...
As soon as the tap ran out and you let your summons back on him.. they'd be tapped again, and if the zealot did halfway decenet dmg most of them would be dead by now.