Restaurants can do what ever they like. Long ago, my family had a restaurant in Deadwood, They let “Wild Bill” Hickcok eat for free—as he was the town lawman his presence made sure the lawlessness of the gold rush town didn’t come into their business. Also, it was good to be known as a friend of “Wild Bill”—besides he was “Wild Bill”.
I hear Ben Roethlisberger uses the same pitch to score free drinks here in Pittsburgh.