Fancy cocktail accouterments make for fantastic gifts, and these pickled pearl onions are great in a Gibson (or atop chicken liver mousse).
Despite the classic cocktail boom, Gibsons still aren’t terribly popular. And cocktail onions aren’t particularly well loved either. Just as an example: In most of the bars, a jar of cocktail onions (and a small one at that) typically lasts more than a year. And those bars are making a lot of more of any given drink than anyone is at home.
Unless you know some one who likes a Gibson, or pickled onions in general, I’d say its a risky choice. You’d be better off pickling a variety of produce with a broader use, or with a specific cocktail in mind. Pickled green beans, peppers, and asparagus always go well in a Bloody Mary. Candied citrus peel (or other fruit really) are surprisingly useful in cocktails. The syrup can be used as a cocktail ingredient, and the peel itself is a really flavorful garnish. Candied or liquor soak cherries are a huge improvement on store bought maraschino cherries (which are the devil). Pickled onions could definitely have a place in a package of home made standard cocktail garnishes. A sort of “I am stocking your bar” sort of gift. But on their own, very few people are chomping a the bit for a better cocktail onion.