Ueshiba - mystic, no doubt. Devotee and worshiper at shrines - no doubt. Shinto priest. NO.
White hakama are worn by many kendoka and other koryu folks.
Here's one of jodo
And pre-war, more than a few aikidoka wore white hakama. After the war, it was relegated to Ueshiba and to 9th - 10th dan. Here's Iwata Hajime
, Here's Hikitsuchi and Ueshiba,
I'm told that in this picture Ueshiba told Hikitsuchi that it was an "unholy day" - sort of like "casual Fridays at certain banks. So they dressed down to go bar hopping and get ripped on cheap shochu (O.K., I made that up).
I've attached a picture from a demo in St. Louis. From L-R, there's Will Schutt, Diane Skoss, Meik Skoss, Phil Relnick, Larry Bieri, Dave Lowry, moi, and my student, Steve Bowman. (Why are all those people so little? Well, that's another discussion, I suppose).
Phil Relnick had the microphone answering questions, and someone asked the significance of the different hakama and keikko-gi and Phil graciously and unwisely handed the mic to me. I replied, "Well, the colors of the clothes are symbolize of one's moral intent and attainment. You see these people on my right, wearing all dark clothes, blue or black. They have embraced evil. I, wearing white, have embraced good. My student Steve, here, on my left, just can make up his mind yet which way he wants to go.