I didn't much like the concept, actually, as it still leave a massive hole, mainly, that it's just common sense for monsters to pick them off. Smart monsters will weaken the PCs this way, dumber ones will just eat the easiest, non-metal-covered targets. And if combat breaks out while hirelings are there, it becomes a chore keeping track of the minions. (Also, the monsters won't necessarily know to target the PCs, making things easier in the short run, again, this depends on the intelligence of the opponents.)
Having said that, I slapped those traits onto minions. (Not all of them. Linkboy? Nah... Sage is a good one.)