IIRC, that's specifically a Faerie/contractual thing (a marriage being (from the Fae POV) a very contractual affair (oaths &c: "to have and to hold, forsaking all others, from this day forward, 'til death do us part...")). I'd need to go back and read the story to be sure whether Harry was actually that specific in the exposition.
I doubt the Whampire Hunger is affected by the ceremony either way; I certainly wouldn't expect a loveless political marriage to convey any protections, so I don't see why a political marriage would end them.
I think the stuff from Something Borrowed and the Connie and the Big Foot story do a lot to murky the waters here, I've seen a lot of speculation about how that could affect the True Love protection from Whamps. But it's all that, really, speculation, there's no definitive answers yet.
Something that always seemed important to me, though, in Something Borrowed, is that Will was going to make vows thinking he was marrying Georgia. Regardless the bride not being the real Georgia, Will would have been earnest and honest in his promises. So, maybe, that plays a part in the whole thing.
And thinking about that, I honestly doubt Harry would make those kind of vows to Lara, and I know some people would say "but the word of a wizards matters because of his power", yeah, but that's if he swears on his powers, right? which I doubt will be the case here.
Anyway, we'll have to wait and see, but I sure hope to have a more definitive answer on how the True Love protection works in the Dresdenverse soon.
It'd still be just way too tragic, and kind of pointless, to have Harry adquire the physical protection of True Love with Murphy only to lose it one year later. Unless the point is to torture Harry, because how morally devastating that would be, to lose the only thing left from her to Lara of all beings. But that also sounds like how JB is thinking lately, so *shrug*
