I think once dry the Gorilla glue is pretty much inert Vince. I wouldn't worry about using it because only the barest trace amounts should ever wind up in the food. If myou have to flatten I would use skis or a sled and use a router. The issue with walnut being toxic came up before but not sure about the allergen aspect. Nothing definitive about the toxicity was found. The dust is bad but so is oak. Oddly, the trees release a chemical which discourages the growth of other trees around them.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.