I will start this blog by asking a question.
Can a non-practitioner contribute to a tradition?
I'm not going to tell you the answers to this question. That is for you to decide.
When the subject of the European contributions to the practice of hoodoo/rootwork/conjure come up, I tend to hear about medieval grimoires, black cat bones, bat's blood, and the like. What most people may not understand is that these things were not contributed by practitioners. They weren't things that actual workers chose to incorporate into their practices on their own. Instead, these things came from the non-practicing white and Jewish marketers/manufacturers who raped and stole the tradition, denied it was a spiritual tradition, repackaged it as "witchcraft" and then sold it back to practitioners for a good profit. Now where else on the Internet are you going to read about this? LOL
The actual European contributions to the practice of hoodoo/rootwork/conjure were the folk magic and folk medicine practices of the Scott-Irish, the Pennsylvanian Dutch, and a bit of German, English, and other nationalities thrown in. People have this notion that things didn't mix. I also keep reading and hearing from people who incorrectly portray Appalachian Folk Magic, i.e. "Granny Magic", as if it was and is primarily a separate tradition that never blended with either Native American or African American practices. That's not the case folks. People travelled. People mixed. People talked and shared tricks. In fact, and going further, in Harry Middleton Hyatt's material there are accounts of multiple whites working as professional hoodoos, taking on paying clients. I have no proof but I strongly suspect that most of these white practitioners were of Scott-Irish ancestry. So this notion of "pure" this and "pure" that is a myth. Things got blended. Was it a perfect homogeneous blending? I don't think so. I think there were regions where either African American, European, or Native American practices dominated. I tend to think that around these regions occurred a lot of blending.
One more thing on the medieval grimoires. At the time they were introduced by non-practicing marketers, they were considered to be "witchcraft". This is a big clue as to how these non-practicing marketers viewed the tradition. Remember, at this time Wicca and Church of Satan didn't exist, so the closest thing that people identified with "witchcraft" were the medieval grimoires and texts giving instruction on how to summon, control and make pacts with demons. Such has absolutely nothing to do with hoodoo. These books were viewed at the time as being 'satanic' and 'demonic' and they reflected how the non-practicing marketers viewed the tradition and not how actual workers did.
Now, readers may counter that practitioner began to incorporate this stuff into hoodoo and they are right. This is how the marketer acted to destroy the tradition, by making practitioners dependant on them and by repackaging the tradition as "witchcraft".