Any service worker who also handles fractional product (coffee beans, dough, raw foods, etc.) Would be considered directly productive, as in they are working a physical thing with labor to turn it into another thing.

I can maybe see their argument working with table servers, but that just means they have a poor understanding of labor and the social content of it. Yeah service work is kinda bourgeois, but it's still social work. They're still adding value to the product (food and beverage) through their labor of social interaction and last foot transport of the food to the table.

Ideally these sorts of jobs disappear under communism and are replaced with more cooperative eating arrangements (canteens, community kitchens, cooperatives), but do they really think that the workers not being unionized will help with that? Labor is labor is labor, no matter what form it takes, if it's organized it has power.