Yes, I think so. However, Deguchi is nothing if not flexible in his theology, so it is also Ame no Toko-tachi-no-kami. After Deguchi returned from Mongolia and started Reikai Monogatari, he needed to please the government authorities and align his theology with the emerging Emperor system, so he finds a place for the Divine Grandchild and for Ama Terasu o Mikami.
Once again you can tell where I am at by what I talk or ask about . . . Hey! I'm a slow reader!
When you say "for Deguchi, the Great Universal Deity; later, the Divine Parent = Amaterasu-o-mikami" do you equate "Great Universal Deity" with Ame no Minakanushi no o kami?