For any legally produced pokeballs, it just won't work on a human. There is a built in lockout on human DNA and while Pokegirl DNA is similar, there are key differences between even a strong-bloodgifted human and a pokegirl. A pokegirl could concievably use one to keep another pokegirl in check, but since she couldn't be a tamer as the captured girl would legally go to whoever the tamed pokegirl is registered to.
However, with illegal modifications, it IS possible to capture humans, but since the pokeballs are hardwired for pokegirls only (and any information about what circuits contain that information is such a high level secret that even getting close to it is warrant enough for death), the result of the illegal modifications will turn a human into a random pokegirl, most likely an Ingenue (unless it's programmed for a specific pokegirl type). For bloodgifted individuals, it's whatever is closest to their genes.