In most of its Pokedex entries, it says that Victreebel's acid can dissolve anything. Why won't it melt James into a pool of James and a Team Rocket "R"?
However, Pokémon is predominantly a children's show, and having Victreebel swallow James and then spit out his steaming, dissolving corpse would be way out of bounds.
James' Victreebel has a permanent dry throat.