I suspect that anyone with a severe, life threatening allergy won't eat something prepared in an unknown kitchen in case of contamination.
But it would be polite to label things as 'suitable for vegetarians' or 'gluten free' if they are, so that people who do have allegies and intolerance can eat something and know it's OK.

My son-in-law had serious stomach problems for years (all sorts of tests) until he cut out gluten. My grand-daughter is only gluten intolerant. Stomach problems as a baby, now she can eat a little but has noticeable behaviour problems if she has much.

And a child at the Playgroup I ran was hyperactive unless careful watch was kept on his diet. Very disheartening when some dismissed the mother as neurotic. She knew that her son had problems that his older brother did not.