Ah, another example of 2nd edition's need for an editor or two more. Don't get me wrong, I do love the system, but things like these crop up. Having read up on needlers in the 2nd edition book, and armor in both 2nd edition and the companion, it does come off as a little confusing. The way I’d rule it, is that the needler does full damage If any part of the body is unarmored actually. This is balanced by that it doesn’t roll for hit location, as it hits the whole body, which means that it can’t do critical hits, nor can it exceed damage thresholds, as it’s not limited to a particular limb. If all parts are armored, I’d go for the spot with the weakest armor for the modifier to the damage.
I don’t know if that makes sense, but it’s my take on the needler.