That definitely sounds like an interesting idea! Looking at nature, different species of snakes can have several types of venom, one being neurotoxins that influence the nerves. It wouldn't be completely out there that a fast acting agent alters the brain, causing it to become psychedelic. Snake venoms and cnidaria venoms consist of many components with their own working and are so potent because they just fire hundreds of chemicals at you, each with a different working, and in our own (real life) society, often new medicines are discovered by separating the components and testing their individual workings.
The one roadblock I can see is why they need to be killed and have their saliva glands removed in order for the venom to be extracted for medical purposes. Wouldn't the purpose of such a venom be used for split second defence, making a venom that's so slow it's more efficient to just kill the creature to extract it be a bit counter-intuitive to their purpose? A more likely scenario would be that they are captured alive and are used to harvest the venom. Maybe the mass capture also led to a large part of the population dying if the researchers weren't careful enough to ensure the wild populations could live on? Alternatively, maybe they store the component within their body, and it's easy to kill one off and squeeze a whole lot of it outta their skin.
It also can help to reason why, if both populations are sapient, they didn't communicate and strike a deal to sell this venom instead of resorting to the killing of intelligent beings, something I can't see many intelligent species resort to easily. Answering this question can add a lot of interesting worldbuilding to both his species and the antagonist species, as well as their cultures and interactions ;v;
(One small thing to think about would be how their own venom acts as a medicine to their own species even though they are immune to its effects, seeing as they don't seem to suffer the psychedelic effects from swallowing the venom they produce, if I'm reading that right! If it's a soft science system you can disregard that notion, but in a hard science system it can help thinking about this <:)