Dialogues:

Cpt. Curious: I do not mean disrespect, but why are you doing such a thing for us? We are soldiers, tools of war, created to fight, and etherefore expendable.

Voolvif Monn: I value all forms of life, be it born or created. Do we not stand side by side on the battlefield? - How are the Benathy doing? Are they recovering from their captivity?

Medic droid: Indeed, they are, Master Jedi. - Although...

During a scan of the inner organs to search for possible poisonings, we have found spores of a parasitical fungus, that actually can be found on Felucia, where it befalls Rancors. It takes over their neural system and forces them to wander to a certain place, where the fungus starts to grow and kills its victim, before spreading new spores.
This spores here had been modified and contain microchips with some kind of remote control system.
I assume, the separatists captured the Benathy for experiments, to test the parasite upon them. Maybe, they wanted to create willing soldiers.
Another possible explanation would be, that the Benathy were supposed to serve as "curriers", that they should infect someone... or something else with the parasite.
Unfortunately, all data, that could have enlightened this mystery for us, had been deleted by the droids, before the battle.