Yes, Ozymandias, you point out the rationale for the Clergyman being a corruption-reducer rather than a straight producer of beakers, gold, or shields, in that if you reduce the corruption of a settlement it will produce a bit more of taxes, or some other type of productivity. Since it's not as good as a Policeman, I made it a hybrid. I suppose other "hybrid specialists" could exist, given a proper rationale. Alpha Centauri had transcendants, for example. Within a Medieval European context, theologians of all three Abrahamic faiths would be the scientist-types. The last vestiges of paganism remained in England as cunning folk and Welsh bards, but I don't recall any Lithuanian shamans or Spanish brujas coming forth with insightful treatises on biology or astronomy during this time period.
Sure, the specialists in this post look like Catholic priests, but that's because the game itself is Americana-centric. I've not seen a Japanese or Indian version of the game, but I doubt the specialists are Asianized to account for the target market of these versions of Civ III.