Yes, that can and may happen, but I can pretty much assure you that it’s a true work of God in those matters.
Of course with everyone, it still is a true work of God, because it does take the Holy Spirit to do his work.
Even though it does take the Holy Spirit with everyone, with most ... a casual observer can almost be fooled into thinking that it was simply related to that Christian (alone) ... giving the gospel, and that’s all it was. Of course, that’s not true ... as it takes the Holy Spirit in each and every individual.
BUT with so-called “witch doctors” (and those over here who do insistently propagate doctrines of demons, incessantly and loudly reject the Gospel) ... with them just about everyone can see it’s truly a miracle that is outside any human agency ... that can bring someone like that to a saving faith in Jesus, according to the Scriptures. Most everyone sees that this sort is the work of God alone.
SO ... if one were to go to the deepest jungles and see a witch doctor, even though that witch doctor may have heard the Gospel many times, especially if someone is going around to many other people in his community ... this missionary is normally going to be rejected right away. At that point, the Gospel has been given and that witch doctor is “on his own” according to the decision he has made. There is no more requirement for the gospel to be given another 100 times to him in order to harangue him to death.
If he comes to a saving faith in Jesus as his personal savior, it will truly be “a work of God” and no one else. God may bring that person around ... and then again, a God may simply harden his heart as God did with Pharaoh. We don’t know and we don’t need to know. That’s not our business.