Victor Hubbard, or "Tío Vic" to the García sisters, tells everybody he's a diplomat with the U.S. State Department. But really he's a CIA agent. A CIA agent who has been sent to the Dominican Republic to overthrow the government of Rafael Trujillo. Oooh, cue the intense synth-string spy music.
Vic rounds up "every firebrand among the upper-class fellas the State Department wanted him to groom for revolution" (3.1.45). But then his "orders changed midstream from organize the underground and get that SOB out to hold your horses, let's take a second look around to see what's best for us" (3.1.45). In other words, the revolution is on hold.
So yeah, Vic's character serves a pivotal role in the fate of the García family (and the plot)—he's the one who gets Carlos García into this mess, and he's the one who gets him out of it. He helps the whole family escape to the United States.
But Vic has a bigger role. He represents an entire chapter in the history of U.S. intervention in Latin America. And he puts a new spin on our understanding of Rafael Trujillo and Dominican politics in the 1950s and '60s. It seems the U.S. had an awful lot to do with keeping Trujillo in power. How scandalous.
Victor Hubbard is also a dirtbag. He takes a different Dominican prostitute to bed every night, and wolfishly ogles every female member of the de la Torre clan, including the little girls. In fact, Victor is every bit as sexist as Dominican men like Manuel Gustavo and Papi:
These Latin women, even when the bullets are flying and the bombs are falling, they want to make sure you have a full stomach, your shirt is ironed, and your handkerchief is fresh. It's what makes the nice girls from polite society great hostesses, and the girls at Tatica's such obliging lovers. (3.1.51)
Looks like Dominican men don't have a monopoly on being macho. This also gives us foreshadowing (or would, rather, if the book was written linearly) of how the García girls are eroticized as Other; how men in the United States will tend to view them as "fiery Latinas" or "repressed Catholic girls" rather than simply people.