They are not chipped, just a plain mug on the honor system. They do not hold as much as the mugs at Typhoon Lagoon at WDW, that's for sure. We were there about a month ago, and the ice machines at Ulu cafe routinely ran out of ice around lunch time and often were not up and dispensing ice again until late afternoon. I was not happy with that, and the other stations are across the resort. The one at Ama Ama was never even used, at any time when we went by. The Lava Shack one was a bit more used, but still much less than the one at Ulu. I wish there was one down on the beach, as the cups don't hold much. I still felt it was a good value as we were there 9 days. My dad loved the coffee from Ulu and sought it out every morning.
I don't know what the official rule is on reusing the mugs. This was our first visit, so we had the current mugs. But I saw lots of mugs there that were different designs than the currently-available ones, and I assumed those folks brought them back and were re-using them. Again, I am not sure this is officially allowed, but many people were doing it.