You need to wear the mask. Worn mask gives you a visible buff against effects from 5 stacks forward.
Would like to know what 5 and 6 stacks drops are though. Dulfy? Anyone?
This we can confirm to not be true. Nothing in our logs registered Dread Touch and people wearing the mask took just as much damage as those that did not.
Some sort of amulet was datamined and believed to drop off 5+ stacks. While it's uses are unknown, we speculate that it will be used for some sort of optional 16-man only boss in NiM TFB when it launches (secret cave). Once again, this is all speculation so nothing is set in stone, but currently it does not look like there is any benefit to wearing it for current content.