In purely philosophical terms, you could say it's "scientific." But... in practice science is an institution as much as it is a method. In that sense "unscientific" means that something doesn't come from the scientific institution/culture.. regardless of who is on what side of a Karl Popper test of science.

I would say that on very practical terms, one could call it scientific, taking advantage of a situation that made possible an trial that could not have been approved as a fully-controlled clinical experiment, given the official opposition to Takaki's ideas.

Takski's hypothesis also met Popper's criterion for falsifiability, and the Tsukuba could have suffered similar beri-beri rates as did the Ryujo.