The response I received when emailing Huy Fong :
Our vinegar supplier has ensured us that the vinegar used in all of our sauces is gluten-free.
I had just generically asked if the sauce contained gluten and the response was focused on the vinegar. I have to admit, I am a bit confused about the whole vinegar thing. I have read a couple of different thoughts about it. I guess I need to check with the company that makes the white vinegar I have in my pantry. I think that other kids of vinegar are ok. But I am really not sure??
Updated to add this from here:
Note About Vinegar - Most Celiac Disease Resources state that the distillation process would remove the gliadin and that distilled vinegars are now safe for people with Celiac Disease. The Celiac Sprue Association advises being extra cautious if you are newly diagnosed with Celiac Disease, and they recommend waiting until the gut is healed before proceeding to use distilled vinegars.