Neither a soilder nor a thane is a priest. However, you can upgrade a thane to the a priest of Kilmorph, which is called a Stonewarden. I think this requires gems and the technology priesthood, but it might be a different tech. Most religions' priest would require the same tech, but a different resource (I think they all need inscense now, but this may soon be changed). Al the priest have unique names. For the order, it is Confessor and for The Ashen Veil its Ritualist, but I don't remember the other priests' names at the momebt. In .20 they all upgrade to either a high priest (with inscense) of an inquisitor, but unique high priests (and patriarchs) are going to be added to .21