I think Ueshiba would have studied with Deguchi with as much fervor as he had with Takeda.
My understanding is that for O'Sensei, Deguchi was THE teacher. Omoto teaches that art is the path to spiritual development/understanding. Omoto believers choose a form of art or two and work to develop it. Ueshiba had practiced martial arts but that did not satisfy. It was when he met Onisaburo that he found his path, which he then followed the rest of his life.