Hell YES you should say something! That's unacceptable!!!
Let me mention one thing before I go on, though. Horses who have runs will STILL burn to death if the barn catches on fire. You know why? Because for some horses, their stall is considered the "safest place." I have heard of more than once incident where a barn has caught fire, and horses with runs died because they refused to leave their stalls. One man in particular was in the stall with the horse, pushing it, pulling it, literally beating it with a whip, trying to make it move and leave the stall. It wouldn't budge. The man almost died as the building tumbled down around him. Unfortunately he had to leave the horse, and it did die in the fire.
If I were you, I'd use the "2 questions, and a zinger" approach. I'd pose the question to your barn owner like this:
"Excuse me, _barn owner's name_? I have a couple of questions. Hay burns hot and fast, correct?" And her/his answer should be, "Yes." Thn you ask, "That's why we keep it away from all hot things/flames/etc., correct?" And again, their answer should be "Yes." Then the zinger; "So why is the trainer/farrier/manager allowed to smoke in the barn, around the horses, and around the hay?"
You have to ask 2 questions that must be answered with a "yes". Your barn owner might think you're an idiot at first, but who cares!
This is serious! If the owner acts like this is no big deal, then I'd inquire about her insurance, and ask for their number. If she asks why, I'd say, "Well, I was just going to inform them about your decision in letting 'so&so' smoke in the barn, around the horses and especially around the hay."
Then, needless to say, I'd move!