i like the theory of the eyes flashing when vision modes changed or when you zoom on the bio helmet,
dont think they would bother instilling fear, maybe as its a sudden change in something the cloak cant keep up with it.and so it flashes and then the cloak catches up and hides it again, i would assuime if they are cloaked and put the tri dot targeting light on that would show up aswell.
as for the non acid proof blades, it has been suggested in some pred novels that they fight each other to get the best weapons, maybe celtcis blades werent the best ones and so werent acid proof