Purity verses taking what works
I don't doubt that O'Sensei had a very Japanese view of how things should be and how martial arts should work.
As far a learning things on his journey, he is very specific about being a disguises traveler who tried not to draw attention to himself, which would leave no time for training in martial arts.
The fact that he learned many things from other teachers is well documented, and adapting them in the forum of Japanese arts appear to be his only concern when face with other fighting arts that could possibly overcome his fighting skills.
It is a great probability that his urging his students train, study, and practice diligently were his words of warning about the tricks or deceptions they might face with other fighting arts.
No ... I don't believe he consciously or physically trained with any masters of martial arts while traveling, even if he did observe other styles. It would have been a footnote to close any gaps in his own techniques and skills, that is the extent of conclusions I must draw from all the different materials I have read on O'Sensei's trips abroad.
We, as modern students, do pursue simularities of other asian arts to the genesis of this art we call Aikido, which is like tracing the history of warfare over the last three thousand years in a forum of transistion because of needs.
Our present study, may indeed, cause new additions to our Aikido, but as far as O'Sensei, I believe he stayed strickly in the Japanese section of martial arts.