I think you hit the nail on the head, about research not being done because the commercials aren't interested. Applies to lots of subjects here, not just cedar shavings. Heck, we worm with cattle and goat meds. You read what you can find, and sometimes take your best guess, or rely on anecdotal evidence more than you'd like to.
I've read before of young chicks dying when kept so they were breathing a lot of cedar fumes. We had some leftover cedar shavings and I've been using them in my coop (of adult chickens at present) but they are scantily scattered over poop and pine shavings, and the coop is so well ventilated it's in effect a three sided coop, because of my climate. Some cedar is much more aromatic than others, too. I use pine shavings for the most part, but if a bag is really aromatic, I'm careful how I use even that.