No. Capuchin monkeys are omnivores, not herbivores. They eat a wide mix of plants and animals: fruit and nuts make up much of the diet, but they also take insects and other invertebrates, and sometimes small vertebrates such as lizards, frogs, birds, or eggs.
For white-faced capuchins (Cebus capucinus), field accounts summarized by the University of Michigan Museum of Zoology’s Animal Diversity Web put the mix at roughly 50–80% fruit, 20–30% animal material, and about 10% other plant food, with the balance shifting by season and place.
Source: Cebus capucinus (white-faced capuchin) — Animal Diversity Web