I'm not a fan of blank firing weapons on the field in any capacity. They sound, um, "distinct?" when compared to arty, arty sims, flash bangs, flash bang trainers, firecrackers, or what have you.
Aside from the easily mitigatable safety issues (BFAs, two-man mag verification, pat-downs for live ammo), they make my lizard hindbrain twitchy as all hell, because it knows damn well that mine only shoots pellets, and remembers what it was like on the other end of the muzzle. This causes me to be less than gruntled.
Knowing that blanks will be fired at an event is something that will make me strongly consider avoiding an event. Not knowing that blanks are going to be fired at an event would lead me to be incredibly unhappy if I found out on the field.