Can you imagine how much sh*t a company would get if an item they made for tanks ended up not being tank safe when used as it was made to be used? They'd be sued for sure. No, that simply isn't something they'd be stupid enough to risk, I don't care how much money they might be saving in production cost by doing so, the potential loss to the company would be too great. Especially when you buy a decoration from Petsmart or somewhere like that, it is going to be safe, because then not only is the company that makes the product liable, but Petsmart is also liable if something goes wrong with the product. Any coating the ornaments do have, believe it or not, has to be tank safe; it is in the best interest of the manufacturing company for it to be so.
Of course, they don't intend for you to boil it or anything like that before putting it in your tank, so if it releases a noxious chemical after you do that that's none of their business; not that I can see why that would cause it to do so, just saying...