So lately I have been wondering "What is Xens ecosystem and society like?" As for the society part this is just my interpretation. Life in Xen as seen in HL is separated into different castes - Slave Caste - Warrior Caste - Noble Caste Vortigaunts are in the Slave and Warrior castes, they are used for laboring in the factories to create the superior Alien Grunts, and to use other machinery like the Thumpers. They are also used as light infantry due to their lightning attacks. Alien Grunts are strictly in the Warrior castes and are NOT made by normal means (duh). They seem to be hybrids of DNA using Vort, Controller, and Gargant parts. They can also act as enforcers for the Slave Caste beating them in line. And can also lead them into battle. And finally, Controllers, which are in the Noble caste, they oversee the production of the Grunts and mind control the vorts to keep em loyal and obedient. Due to their similarities with the Nihilanth, it is no wonder they are deemed Nobles in the hierarchy. I would also assume some of the creatures in Xen are domesticated such as Gargants, which seem more like animals. And Houndeyes and Bullsquids, which could be used as some kind of guard dog. If I were to implement cut creatures into it, I would make Kingpins put in some kind of generator to amplify a Controllers psionic power, kinda like a Vort Cell in HL2B. Chum Toads would be a common food collected for Vorts to feed on (And by extension Headcrabs as well) And Flocking Floaters could also be used as companions for the Xen Military. This is all only an interpretation so its not what I think is cannon, but its cool to think about, take care.
To add some info on my Alien Grunt claim, Grunts have the following parts: Mouth of a Controller 3 arms like Vort AND controller Main arms resemble a Gargants.