"I can't see anything for Japan now but revolution or military domination. The latter would, I think, be best."
The compelling poetics of Hearn's body of work notwithstanding, those poetics included a wholesale embrace of Japanese militarism.
The claim that this embrace "is therefore also not colored by the ascendant Japanese hypernationalism during the 20's and 30's that tended to increasingly dominate thereafter until the end of the War," is technically correct, in much the same sense that one may correctly argue that a contemporaneous, but partial, diagram of a cause is not colored by a diagram drawn in fuller, but still partial, knowledge of the cause's consequent effects.
A look at some of these issues in Hearn's writing can be found in Daniel Stempel's 1948 article, titled Lafcadio Hearn: Interpreter of Japan here
, if you have JSTOR access.