I am forced to this conclusion since I had no responses to my query a few days previous.
adiaphorist, n. and a.
1. One indifferent about points of theological discussion; an indifferentist, or latitudinarian.
2. Eccl. Hist. A member of a sect so called; moderate Lutherans, who held some things, condemned by Luther, to be indifferent or non-essential.
B. adj. Theologically indifferent.