One thing that has to be overstood is that in Ethiopia around 1930 you had more than Christianity & Islam being practiced in Ethiopia that includes the indigenous belief system which His Majesty never outlawed or prohibited.

His Majesty taught africans to live side by side with ones of different cultures, religions, etc..so InI must live the same way....so if somone wants to to practice Vodou than according to HIM they have the right to do so(whether the bible states if its wrong or right)
...eventhough His Majesty is a devout Ethiopan Orthodox King He chooses to allow ones from outside that faith still worship as the please in Ethiopia.
I will try to find the speech where His Majesty states that His religion is not the only valid religion...what does that tell you(it tells me that anything outside the bible or outside of Je-sus can also be valid)