Everyone says that Zalera is immune to physical damage while his little minions are out on the field. So, I was all prepared for a rather annoying battle against the twerp. As it turns out, however, his mighty shield does not affect all weapons. Balthier is consistently inflicting 4500 points of damage per hit with his Fomalhaut. That's right. Guns, which inherently negate defense, also penetrate Zalera's minion shield. I'm going to check soon to see if other weapons which don't use physical defense to calculate damage work too.
Measures work too, but their pathetic attack and status imbuing nature means they aren't worth it. Poles don't work, unfortunately, despite using magical resistance rather than physical defense for their calculation.