I'll leave it to GL and other, more experienced pilots to comment, but when I've landed a Cessna 152 on a rough "grass" strip, it had no difficulty dealing with a "rough" surface that appeared to me to be comparable to the good-parts of the coral surface shown at Niku. My Cessna only has small tires compared to AE's Lockheed, which looked to me to be able to handle a rough ploughed field without difficulty. If AE landed at Niku as proposed, the big tires would probably have delt with the best parts of the reef surface easily.
Consider this - Alaska bush planes commonly land on very rough surfaces using tires about the size AE had on her Lockheed. They land at speeds about the same as the Lockheed (<60 knots), and I would guess with approximately the same loading (I'm guessing here - Gary please fill in details). The idea that a Lockheed might be able to land on the best parts off the reef seems entirely within reason to me. The unknown part of the question is whether AE would have been able to do so, even assuming she made it to Niku. The best part of the reef might or might not have been obvious from a quick fly-over examination. I'm not aware of AE having any experience dealing with water landings, or the optical illusions they can present. That's pretty specialized training. Fred might have had some experience.