I certainly got the vibe that name inheritence (and in some cases the procreation of the species) is dislocated from marriage in Eorzean culture.

I need to correct you on the keepers. Their matriachal society holds that the mother's name is inherited and, like with the Seekers, the societal structure would probably collapse if males were tied to monogomous relationships for the purposes of mating - their name is from their mother, not their wife.

The Elezen may be the interesting exception, but it is not clear how their names are inherited.