Stray toughts, fwiw:
1) Shinto vs shintao: point clarified in another thread very nicely.
Another point pertinent is convention: Shinto is just spelled that way the same way that judo is spelled like that and not juudou or juudoo.
2) Osensei as priest.
Omoto, following the pattern of many "new religions" has a flattened hierarchy with many lay preachers. Judging by what we know of him through his students' interviews, Osensei certainly preached. But hard to hold to the idea of him being a priest when Omoto probably has nothing quite like that category.
3) Omoto as Shinto.
Shinto underwent a decided mongrelization coming into Meiji, ironic as Tokugawa just before it was a period of intended purification of "foreign elements" (Buddhism). Trembling at the impending threat of colonization by Europeans, foretold by Perry's hubristic gallivanting into Uraga Bay, the Japanese wanted unity to repel the foe and used Shinto as a means to this end. Having tried to destroy Buddhism (many Buddhist monks simply shed their monastic robes and put on priest's clothes), the authorities demanded that religious expression fall within the purview of State Shinto, ie, join a shrine system or disband. Deguchi had actually gone to Shinto school (for 2 years, IIRC) and so qualified. But his actual practice was more in line with shamanism than the ritual of Shinto, and could be considered Shinto mainly through political posturing.
A post to archive on the subject, is Wm Bodiford's at: http://www.e-budo.com/forum/showpost...9&postcount=18