It depends on the state of the banana in question..
Green-peeled bananas are basically all-starch, the actual fruit itself. Most of the enzymes that break down this starch into sugars are still located within the peel.
Yellow-peeled bananas are still mostly starch, although the enzymes are starting to make their way into the fruit and change those starches into sugars.
Yellow-peeled bananas with black mottling are even less starchy, as the enzymes are moving in a bit of an exodus, towards the fruit at this point. The darkening of the peel comes from the breakdown of the cell walls and oxidation of those cells; basically the peel is deteriorating as the enzymes and nutrients head toward the fruit inside.
Once the peel is blackened, it's basically given up everything it has to offer and without processing, the fruit will rot in short order. The peel at this point is completely oxidized, has lost a majority of its mass, and is barely enough barrier from the atmosphere to protect the fruit inside.
All this said, personally, I dont think I'd ever use anything less than a mottled banana in my wines, simply because there's too much starch vs sugar; if the peels are blackening, I dont feel comfortable with using them (the peels) in my wines... Basically, I'll always ripen the fruit until the peels are atleast partially black, and I'll probably never include the peels.
How this all plays into what they spray on the bananas, and if those sprays work into the fruit alongside the enzymes.. I have no idea... All I know is this small batch of Banana Bochet smells amazing - the bananas have overwhelmed the caramelized honey so far..