No, breweries are not required to give samples. But imagine this scenario.
Attendee #1: "I would like a glass for $10." Brewery: "Thank you. Please enjoy our complimentary beer." Attendee #2: "I would like a glass for $10." Brewery: "Thank you. Please enjoy our complimentary beer." Attendee #3: "I would like a small plastic cup to try your complimentary beer." Brewery: "I'm sorry ma'am, but you must pay $10 for one of our glasses before you can have our complimentary beer." Attendee #3: "You are giving everyone else complimentary beer. The DOR rules say you cannot refuse individuals solely on the basis of their not paying for one of your glasses. You must have a different reason for not serving someone that applies to everyone, or serve no one."
So how does the brewery handle this? Well, there are a few comedy options:
Brewery: "Well ma'am, we just do not serve to those who...are wearing a black tee shirt with...dark wavy hair. I totally did not just make that rule up. And we will totally enforce that on that other woman with a black tee shirt with dark wavy hair in line who happens to be holding a $10 bill in her hand. Yeah."
Brewery: "Well, you found our kryptonite. Sorry everyone, brewery's closed! Please file out the exists and have a great evening!"
Or they can do what most reasonable people would do.
Brewery: "Fine, here's your cup. It's not like we're going to go out of business because of the 1-out-of-50 or so that shows up without money."
So yes, a brewery could just flat-out refuse to give free samples ever, but they would be missing an opportunity to sell glasses to the vast majority of people who don't mind losing $10 so that they do not have to fiddle with the really inconvenient 4 oz plastic cup. Free rider problems aren't normally problems from a business perspective when the free ride is bumpier and less pleasant than the paid one. They may be problems from an ideological perspective, though, but I doubt your average brewer has a copy of Atlas Shrugged close at hand to help him make business decisions.