I've been doing a lot of research about candi syrups, and commercial caramel syrups in general. The bad news is something I've come across on the FDA website about "process aids" not needing to be disclosed. Sugar by itself can't darken the way those syrups do. Maillard reactions need a nitrogen source and a reducing sugar. Since the nitrogen is consumed, and the acids, bases, and (usually) ammonium compounds used to make the syrup are "process aids" they don't have to list them on their ingredients.
But I haven't come across anything in my research to suggest they use gluten in their process, although it would certainly serve as a nitrogen source and probably could be used.