[Excuse him if he looks a little confused; it seems strange something like that would be kept a secret. Maybe poachers were interested in it, if they were valuable? Or people were afraid of them, and wanted to decimate the population?]

It'd probably be dangerous if you just let a wild Pokémon do it, I suppose, or one you don't have a good relationship with. But the Pokémon that do that kind of work all have trainers! Or at least an organization they work for, like a hospital. If they don't have certification, then they're likely just doing it for their own trainer, so they won't hurt anyone.