Has anyone ever fermented fresh coconut or its water and produced an edible probiotic that tasted good and did not make you sick?
In a word, yes.
According to MakeSauerkraut.com (of all places)
To make fermented coconut water, the sweet water is mixed with a culture (milk kefir grains, water kefir grains, whey from yogurt or a powdered starter) and left to ferment for 18 to 48 hours in a warm place.
There seems to be a lot of recipes out there for such a thing, a quick internet search for "ferment coconut water" should yield more recipes, methods and the like.