Yes. Gluten is a protein and it does not carry over in distillation, so wheat and rye vodkas test the same as potato or grape vodka and grade A here. The wrinkle is labelling rather than chemistry: US alcohol labelling rules will not let a spirit made from a gluten grain carry a plain "gluten free" claim, so a bottle you can drink safely may still say nothing on the label. Flavoured vodkas are the real exception, because anything added after distillation is not covered by the argument.

It is the lowest risk alcohol we grade, at B rather than A. The distillate itself is essentially free of histamine, unlike wine or beer, and it adds no sulfites. But alcohol interferes with the way the body clears histamine and dilates blood vessels on its own, so people with histamine intolerance often still react to a neutral spirit, just less severely and less often than to a glass of red or a fortified wine.

Congeners. Dark, barrel-aged spirits carry many times more of these fermentation and cask by-products than a filtered neutral spirit, and studies that gave matched doses of bourbon and vodka found worse next-day symptoms after the bourbon. Vodka is not harmless, and the total amount of ethanol still matters most, but at equal doses it gives your system less to process.

Not meaningfully once it is in the bottle. Both are distilled to the point where the starting material leaves almost no trace, and both grade the same across our criteria. Potato vodka is worth seeking out mainly for peace of mind if grain spirits make you anxious, or if you react to the idea rather than the chemistry.