My understanding of history is that, by the time Ueshiba had established his own dojo in the 1940s, Kano and Funakoshi had already popularized budo that were practiced without hakamas. Furthermore, many of Ueshiba's students came to aikido after first training these budo. It doesn't make sense to me to believe, in that context, that it went without saying that budo and the hakama were inseparable.
Yes, also both Funakoshi and Ueshiba sent teachers to the army's secret services school, where I believe MI and civilian spies trained in their own clothes. See the movie "Kuro-Obi" (should be available on YouTUbe) for a dramatization of army practicing karate.