What does it mean "don't do this to yourselves"? CM is "supposed" to be Medium Role Play level so you, as a player in game, are supposed to act on a knowledge your character has. In-da-lore lowly marines don't know that preds exist, its their first contact. So "Predator" and "Yautja" falls off from the terms you can use.
"Aliens" is just a term for something foreign, particularly about something from space, so its legit. The funny thing is - Nobody calls benos "Aliens". Not once in my few years of playing I have noticed that term being used.
Walking Dead avoids "zombie" just for the sake of branding and to be snug about it like "Heeeeeeeyyyy... That's not a 'ZUMBIE' or whatever, its 'Walker' ughhhhhh!"
You want to be LRP? Then there are few other combat servers where you can freely call everything by any word, even those forbidden and deemed racist.