I looked at the parts catalog for 2017 and it shows the Kohler. I guess they put as much effort into updating the website as they do supporting the stuff they sell.
I'm not convinced that emissions compliance was the sole reason for the change. John Deere is still selling Gators with the old Yanmar 3TNV70 and lawn tractors with the Minimax. I suppose Deere has a better relationship with Yanmar and Polaris got a better deal from Kohler.
I also just noticed Yanmar is selling UTVs now. It looks like a re-badged Yamaha. No diesel option.