In his memoirs, Yasuo Kobayashi, an 8th dan who was uchi deshi at the time, speaks of a very warm convivial dinner in 1958 or 1959 where Mifune and Ueshiba had a long conversation about the differences between aikido and judo. So the attitude of Ueshiba toward Mifune seems to have been respect and friendship, not avoidance. Actually, the two should have gotten along; Mifune's waza is the most "aiki like" of all the judoka I've ever seen.