No idea why Dove would recommend vinegar as it contains gluten. I would imagine it would be OK for coeliacs as they can have small amounts but gluten intolerance & autism is a different ball game.
Maybe they mean wine vinegar (no grain, no gluten)? or maybe the vinegar you get in downmarket chippies? - it's labelled 'non-brewed condiment' which I suspect means it is industrial (synthesised) acetic acid watered down and mixed with a dash of caramel.
I suppose it may have been bio-ethanol once but I can't see a big hulking molecule like gluten getting through a distillation process.
Actually I can't see something that big getting through the fining (sedimentation) process either - it is used to make all commercial beers (except weissbeer - which I dislike anyway) - beer which is then soured to become 'real' malt vinegar.
The easiest way to settle this is for someone gluten-intolerant to drink the most non-'real' beer available (cheap lager or overpriced US beer) and then progressively try more and more tasty beers until symptoms appear.
Joking aside - I always assumed the suggestion to add Vit C to boost yeast activity was based on its anti-oxidant properties (healthy, fitness-obsessed yeast cells?) but maybe a slightly lower pH also helps them? Most yeasts almost certainly evolved in rotting fruit - which is a lot sharper than rotting grain...
Cheers.