The company has set up transportation for the crewmembers. They negotiate and PAY for the services that will be required. Our contract states that if food is not available, the hotel will provide transportation to meet the dietary needs of the crew.
When Joe the sales man takes a client out to dinner does he tip the server with his own money? NO! He adds it to the company expense report. When my airline reimburses me for tips to van drivers I will tip them. I don't pay to work, I work to get paid.
PS I waited tables for over 10 years, I know how tipping works. I always tip 20%+ because they have to claim it all. Unless you pay for the meal with a card and tip with cash, then uncle sam won't know

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Van drivers don't submit weekly tip reports to the hotel for tax purposes. If they don't get taxed on it, it's not a legal source of income.