Closest I've come to a called ace was during a doubles tournament. Someone hit an ace in the first round, and we were talking during lunch and I told him I was going to take half his ace pot during the second round. So about halfway through the second round, my partner threw first and shanked his drive. He got mad at himself and started apologizing to me, but I calmly responded "no worries, I've got this." and stepped up on the tee. Big hyzer shot over the trees and a few seconds later, bang, right in the heart of the chains. When I said "I got this" I wasn't really calling the ace, but in my mind that statement and the prediction at lunch make for as close to a called ace as I'm going to get. Best part was Mr first round ace was playing a parallel hole and saw the whole thing, so I got to play the I-told-you-so card right away as well.
I had a kind of premonition about another ace. I was practicing the week before another tournament, but it was not the tournament course. On one hole, I threw a shot right up the gut, and for some reason, a random thought crossed my mind. It was that if I replicated that exact shot on one particular hole at the tournament course, it would make a pretty good ace run. Fast forward to the tournament, also a doubles tournament (and coincidentally, I was playing with the same partner), and we get to the aforementioned hole. I visualize trying to replicate the throw from the other day, and throw my drive. It looked nothing like I pictured, carrying well left of the line I wanted. Oh well, not getting the picturesque ace this round. Then it hit a tree, took a sharp right turn and bang, right in the chains.
I've only seen one "called" ace and I wouldn't really count it as an ace, but the guy who threw it seemed to count it. I was giving a tour of my home course to Dave Feldberg when he came to town to play our B-tier a few years back. We were on the fifth hole and we'd each thrown a drive when he asked if this hole was one that people tried to intentionally skip their drive on. I hadn't seen anyone intentionally skip a shot since it is about 170 feet with a slight right to left turn...even beginners reached this hole fairly regularly in the air. So after that, he reached into his bag, pulled out a huk-lab dyed something, and said "this is my ace disc, I get aces with this". Then he skipped his shot right into the basket. A nice practice shot, but not a true ace. But after our round, he was describing how he shot and while he wasn't keeping score, he estimated he shot "-11 with an ace". Seemed he wasn't just counting that second drive as a ace, but he was counting quite a few second and third tries, both drives and putts, when estimating his score. That amused me. He shot -5 and -4 during the tournament to win it, so apparently he wasted his "hot" score on the practice round.