I hope you guys don't seriously think ZUN put as much thought into all this as fans have.
Are you kidding? Go wash your face and read CoLA 25.
If there's one thing ZUN has shown over the years, it's that he loves sticking little details like this in on purpose. c.f. Kanako and Suwako's relationship being based on the kamiyuzuri from the Kojiki, why Yukari's name is Yakumo from CoLA 25, why Lunarians are basically immortal, why the flower incident happens every 60 years from the Seasonal Dream Vision short story, etc. If ZUN introduced a new character as "The One-armed, Horned Hermit - Kasen Ibara (Kasen Ibaraki)" and made her story so that it
conveniently shares aspects with that of Ibaraki Douji, an oni who was well-represented in Japanese art in the 18th and 19th centuries and at one point lost his right arm and had to go looking for it, he probably did it on purpose - he's got a record of doing things like that. The real question is what it really means. Too bad this comes out every other month.
Of course, I could be wrong - it's not like it would be the first time!
Well, i don't really know anything about devas except that they are four onis.
The "Four Devas of the Mountain" in Touhou are oni based on characters in the Shuten Douji legend. Their leader was Shuten Douji, and his second in command was Ibaraki Douji. The four strongest members of his band were Kuma Douji, Hoshiguma Douji, Kaneguma Douji, and Toraguma Douji. The only real important thing is whether ZUN goes out of his way to make a connection between a Touhou character and a legendary character. (Four Devas is just one translation of 四天王, which is a ... fairly commonly used term. Groups of characters bear this name in series as diverse as Final Fantasy, Digimon, and Hokuto no Ken.)
In this case, you don't get to be in the group if you're not (or weren't at some point) an oni, since it's a group of four oni ...