"Pair" is a singular noun. Its verb is inflected with an "s." In this hed, that would be: .... pair exchanges vows.
The kids on the copy desk were probably thinking "couple," which can be cast variously as either singular or plural, depending on whether the editor is a prescriptivist or descriptivist. But whatever they were thinking, Charlotte Sun copy editors page designers wrote "pair." Too bad there wasn't a pair of eyes proofreading the headline on the day's big story.