From the original essay by Henry Ellis:
During our trip, I asked Sensei how he met O-sensei. He said he was travelling across Japan to another judo competition when an old man sat opposite him. He said he was aware that the man was staring at him, and then the man said, "I know who you are!"
Abbe sensei modestly replied "Everyone knows who I am. Who are you?" The man explained who and what he was. Abbe was tired and needed to sleep, but the man continued to talk. Abbe politely asked him to be quiet. The man suddenly stuck his small finger in Abbe's face and demanded, "You are a strong young man. Break my finger." Abbe said he needed to sleep, so he grabbed the man's finger, intending to snap it like a twig. He suddenly found himself on the carriage floor in agony. It was then that he asked Osensei if he could study with him.
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.