At Footnote.com, there's an FBI file for Boris Schumacher Dukan. Date is March 28, 1919. (The U.K. ship also had a name like Dukan in front of Boris).
It is about his application to enter the U.S. and a witness says he thinks Boris is in Mancuria/ Siberia at that time. The FBI recommends he not be admitted.
I think it would be worth a subscription to Footnote.com for you to be able to read the whole thing.
Footnote also has articles in the Chicago Tribune and the Washington Post mentioning his reporting in 1916 about the Russian Army's losses.