Are you looking to run strictly E85? If not, I would assume you can run up to 50% without any problems. I know the 6.0L engines from 2015 up could run up to 50% ethanol blend right from the factory.
I've done a few tests with my 2017 6.2L, non flex fuel, and it handles a blend up to 50% just fine. No lights or weird running. I did notice that at the 50% range, it seemed like it may have run out of its programming limitations for fuel delivery.
This was a blend of 87 and E85. From what I've seen on both yukons, 08, 17, is that they seem to really like a 20-25% blend of 87 and E85. The power is there due to higher octane, and the mileage doesn't seem to suffer too much. Just an idea.