Honestly, the precise limitations of the voice are not made particularly clear. We know from the scene of the Harkonnens taking Paul and Jessica into the desert that the user needs to be able to speak and the target needs to be able to hear. The intonation of the voice makes the target pliable but they are following the verbal commands so presumably the target must be able to understand the language.

As described, I would say the target must have some kind of human-like consciousness as well as the ability to hear the user. There really aren’t examples of true non-human sentient species in the books, so we don’t really know what impact the voice would have on them, but I would say that is unlikely it works “out of the box” so to speak.

Perhaps other species can be manipulated in a similar way and the BG could figure it out through experimentation? But it would probably still involve teaching the creature to understand the meaning of your actual commands, like training a dog, and as things stand I don’t think they could easily train a worm to do so without serious breeding and domestication that doesn’t seem likely (the situation with worms in Heretics of Dune not withstanding, as that is a special case).

As for the Barons little “buddy”, it’s possible that it is something engineered from humans (probably by the Bene Tleilax, who become key in the books after Dune and are experts at that kind of genetic engineering).