Yes, the servers let you know.
That's why Guests (all Guests) are asked if they're using any Dining Plan - so the server can let you know what's included/available, and what's not.
Examples: Chefs de France the beverage allowed is only your typical soda/coffee/tea (okay, fine, probably milk but since I don't drink it...). On the other hand, at Kona Cafe you can get ONE non-alcoholic specialty beverage as your drink, or unlimited soda/coffee/tea... while at Whispering Canyon, the Bottomless Milkshake is counted as a beverage on the
DDP - and yes, even the refills.
So, with SO many different conditions based on the location, the servers really need to (and know) their "stuff", and the Guests have to trust that the servers know what they're talking about.