Indeed, that is so. Only his first incarnation was the Voodoo Man, with a 'vee'. Comic books in those days were required by the postmaster to have text pages, and Kelly wrote some interesting ones for the Pogo comic books. The Voodoo Man was from Pogo #9.
As you'll see, the next time around, it evolved to Hoodoo Man, with an 'aitch', and came back several times as such. And the tie-in to Pogo in Pandemonia is that he truly seems to be a forerunner for Doc created over a decade before Pandemonia. It arouses curiosity as to whether this was an intentional reinterpretation of days of yore for Kelly, or was it a subconscious 'type' that Kelly had lying fallow in his imagination.
For what it's worth, I have the personal memory of Kelly describing to me, in January of '66, that Pogo would be running into an odd little fellow, a magician of sorts. As it turned out, Doc Noah seems to have some weather magic at least, and we'll see here shortly that the Voodoo Man did as well.
All in all, it seems that Kelly had characters and scenarios that he reprised as part of his own personal mythology. When you look at it objectively, Kelly's entire oeuvre was really devised as a unique set of fairy tales, with talking animals and a fantasy wonderland (even with much of that wonderland being a swamp). When I talked with him, he waxed poetic about fairy tales for a good long time, and I have to think that listening to him cemented my life-long interest in fairy tales as well.