There are a few unexplained characteristic inconsistencies between Sin era and eternal calm, I just like to ignore X-2 as far continuation of the story/characters goes. The coupling of these two characters doesn't really make a lot of sense. That is until you consider what Wakka's options are; without re-locating he has to choose between Lulu, that "stay-away-from-the-summoner" whiny old bitch, or one of his Aurochs team mates. I'd still probably choose one of the Aurochs, surely at least one of them has to be a keeper.

I personally think the developers just wanted to cook up a story in Besaid for those characters, to give Yuna and co. a reason to want to revisit, and what a microwave meal of a story it is. Oh well, At least their child won't ever go hungry.

So no, I don't think the characters are suited at all, but given the limited option for potential partners due to their small island with a very small population a relationship born out of convenience could make "sense".