It's hard to do utilitarian ethics without commensurate utility functions, and so utilitarian ethical calculations, in the comparatively rare cases where they're implemented with actual numbers, often use a notion of cardinal utility. (The Wikipedia article's kind of a mess, unfortunately.) As far as I can tell this has nothing to do with cardinal numbers in mathematics, but it does provide for commensurate utility scales; in this case, you'd probably be mapping preference orderings over possible world-states onto the reals in some way.

There do seem to be some interesting things you could do with pure preference orderings, analogous to decision criteria for ranked-choice voting in politics. As far as I know, though, they haven't received much attention in the ethics world.