1. Nope, they can though, it's as Otar said.
2. Yes, and unfortunately you can only penetrate the double and triple shields, so in regard to the +10 penetration rating it has some very big limits to it. About penetration rating you can read here:
http://forums-us.ageofconan.com/showthread.php?t=189860
As for Slaugther the Armor Penetration is the biggest deal, and currently Im experimenting with it in PvE. It seems to depend on the mob you're facing.
Strawman has no armor, so he's not affected. Mobs in Ymir's Pass have no armor left when they're at x5 stacks of torment, so they're not affected by it either if x5 tormented. Mobs in Onyx Chambers are affected, even at x5 stacks, so you need to be up against a mob with more than 4500 armor. It seems mobs can't go into the negatives, however there are mobs in game with enough armor to penetrate through. These are only my mere observations.
It could prove difficult to test properly vs. raidbosses you'd want to use it against, unless... you go in some gimp spec without rampage and no groupbuffs to do the testing without any chance of error.
Use the Internal Bleed dot to test. Good way for bears to check this out.