One common position in meta-ethics is that facts about morality exist, but are not natural properties of the universe but rather are something else. I can't measure the wrongness of slavery the same way I can the charge of an electron; but that does not, in the above view, mean said wrongness is non-existent or unknowable.
However, I can imagine similar arguments being made on other topics, e.g. a theist claiming divine presence is a non-natural property. Is there any reason such non-naturalist realism is less plausible for theology than for ethics?