Welcome to Planet Hell is set shortly after the events in the book Aliens: Earth Hive. No characters from that series are represented here, but it provides a good background.
For those of you who have not read the book, here is a synopsis of the relevant storyline:
Some idiot corporation captured an infected human from a derelict freighter that had ended up in Earth orbit. The Alien within developed into a Queen and started laying eggs. Soon afterwards, a group of religious fanatics (who believed that Aliens were the messiah) broke into the facility and were infected. The resulting hive was quickly stamped out by the military, but too slowly; more hives sprang up everywhere. Earth was eventually given up as a dead loss, and evacuation was begun, mostly of important military personnel, with plans to launch nuclear warheads to try and cleanse the planet. Planet Hell opens shortly before the 'cleansing'...
A few sharp people may notice that although it uses 'Earth Hive' as a background, some of it is closer to the 'Official' quadrilogy. I'll say no more, as it's not particularly important.
Finally, I don't intend to say this for every chapter, as it's not a situation likely to change before I finish this. I have to admit that I don't quite see how exist based on the lengthy rules and regulations section, but disclaimers seem to solve this to some extent. So: I do not own Alien, Predator, or anything in connection with the aforesaid franchises apart from the characters and locations created for this story.
And yes, that does mean that there will be Predators... at some point...