A lot of folks at festivals and restaurants do this. Not so much for the flavor, but for the aroma. It increases the "BBQ smell" drifting out over the crowd by at least 10X. There was (or maybe still is) a fairly famous rib joint in a seaside resort town that attributed their success not to their food or fancy advertising, but to a custom made exhaust system that was aimed at the street in front of the restaurant. I can remember walking by there and it being really difficult not to go in, as the aroma was incredible. I believe I remember reading that they tossed the onion scraps (they were also famous for their fried onion loaf, so went through a lot of onions) into their smokers.
I once tossed half an onion into the coal basket of my mini while camping just to see if it really made that much difference. It did. We had people coming around and snooping most of the day, asking what smelled so incredible.