IMO We know far to little of Ryou, Haki yes, But the Application that As Hyo understood it to be. There might not be a Black Coating for it. To many inconsistencies for my tastes. We should assume Haki is being used, But the black coating is not always there, if it is.
I lean on Kaidou did use Haki, possibly the bare minimum. But again it's my opinion, and it's not held highly here.