So here's the test set up. On the Japanese chisel side, a "delicate" 3 mm Imai bench chisel (oire nomi), about $50 from Hida Tool, which is the same cost as a 1/8" Lie-Nielsen bevel edge socket chisel. On the cocobolo side, a cocobolo bowl blank 2" thick. If you look closely, you'll be able to see how much I overpaid for this bowl blank.
I did a quick touch up of the chisel on a natural fine waterstone before starting. No chips here.
I sawed the sides of the dovetail.
And started chopping.
Close up of the chisel stuck in the cocobolo after a good whack. Notice that the width of the place I'm chopping is actually twice as wide as the width of the chisel I'm using, so I'm really doing twice the chopping I would if I were using a properly sized chisel.
After getting about halfway through, I started chopping from the other side.
All done! Total chopping time was a few minutes, not counting the time I took to take pictures.
No chips in the chisel after cutting a 2" thick dovetail in cocobolo.
Here's what I think is the impressive part. I took a scrap piece of pine, and did some endgrain paring with this chisel, without any additional sharpening.
So hopefully this will put to rest the question of whether a Japanese chisel can be used with very hard woods.