Ah, the wonders of teh internets! Not to mention the kindness of strangers and the generosity of friends! Since I last wrote on a possible Hawthorne/Izumi connection--Izumi perhaps using the crisis of faith and epistemology in "Young Goodman Brown" to add some interesting resonances to his meditation on dreams and reality, life and death in "One Day in Spring"--I've heard back from Charles Shiro Inouye and Susan Napier at Tufts and my friend Koichi Fujino at Seinan Gakuin University in Fukuoka. The bottom line: there's no definitive evidence either way on whether Izumi could have read "Young Goodman Brown" before 1906. In fact, they know of no work in English or Japanese that takes on the question directly.
The Full Metal Archivist approached the question from an oblique angle that may well prove to be helpful. She noted that Izumi's mentor--おざき こうよう Kouyou Ozaki--read a good deal of literature in English and was a huge influence on Izumi in his literary and wider life. So it's possible that Izumi heard about "Young Goodman Brown" from his mentor. Another line of research to pursue.
What makes this very specific empirical question of perhaps wider interest is that it points to a more general problem: when an intertextual reading isolates structural homologies, what ought we to do with them? I speculated with my students in class Friday on any number of directions we might go in to pursue everything from the meaning and significance to the implications and stakes of the structural homologies, should they actually turn out to be intentional allusions on Izumi's part. Clarifying the conditions of possibility for an actual case of translinguistic/transcultural influence/revision can do more than establish a factual base for an interpretive reading; it can also help reveal pathways for transnational communication at the turn into the 20th century.