From the original essay by Henry Ellis:
Abbe-sensei entered the Busen (Butokukai school) in 1932, and graduated in 1936. He remained one year as an instructor. These were the golden years of his judo career. A careful reading of the linked article shows that from 1936 until 1945, he was mostly in the military, and was not competing in judo. In fact, he had a very small window of time in Kyoto when he practiced. After the war - from 1946 - 1956, he was mostly obscurely functioning as a police judo instructor, at which time he went to England.
It is very likely that his time as a student with Ueshiba Morihei was limited. This is far from unique - there are other judo men, such as Kotani, who received rank from Ueshiba - not as purely honorary, but apparently, he taught essential principles and a few waza, which was "stacked on top" of their own high level skill.
As Ueshiba did spend time in the Kansai area - Kyoto and Osaka - in the mid-1930's, it is quite likely that this is when Abbe first studied with him. It is also possible that Abbe continued his studies after the war, when Ueshiba was again traveling frequently to Kyoto and Osaka.
BTW - Abbe's sister, mentioned in the article, was Abe Toyoko, the marvelous shihan of Tendo-ryu naginatajutsu. I describe her in some detail - along with portions of an interview about her time in the Butokukai - in my book Old School. Her nickname in the Tendo-ryu was "gunso" - the sergeant - because she functioned that way, as a top-sergeant to the other shihan and also to Mitamura-sensei, the soke. I've attached a photo of Abe sensei demonstrating a Tendo-ryu armlock - when closing with the opponent, one drops the naginata, and locks the arm, enabling tori to draw a dagger and finish them off at close range.
There is a photo on my Kenshiro Abbe Blog from a news paper with Abbe Sensei and his sister Abe Toyoko, this was probably one of the last photos of Abbe Sensei and his sister together
The war certainly did interrupt Abbe Sensei's carreer. However he did develop JuKendo ( bayonet fighting) for the army. Sensei actually demonstrated this at the Royal Albert Hall London in 1955 at the same event where Aikido was seen for the first time in the UK.
Co-author `Positive Aikido`