Looking around, I found that the first All Japan Weightlifting competition was held in 1936, and the first all Japan Weightlifting Association was formed at that time - so weightlifting must have been around for some time prior to that if it had already spread around the country.

Plus, there are plenty of similar resistance style exercises that would produce similar results, even if not in western fornat.

As an aside, I seem to remember Yukiyoshi Sagawa, who was a contemporary of Ueshiba, as being a big weight lifter at one point in his life.

Best,

Chris