The whole complaint is interesting. The tricky thing about citing claims about ZeniMax's IP is that those claims hinge on the IP actually belonging to ZeniMax. Oculus and Carmack may be able to make a case that the VR work Carmack did isn't bound up in Carmack's work-for-hire agreement with ZeniMax.
But directly using ZeniMax properties to promote the thing while working under a cloud of IP ownership uncertainty was probably not a great move.
While Oculus surely shouldn't have used ZeniMax's stuff in their demo, and should definitely pay some kind of damages for it, it seems like a small part of what's at play.
Or is it supposed to show how fast-and-loose Oculus was with other people's stuff?
Edit At least reading through the rest, and taking ZeniMax at their word, it looks like ZeniMax has a credible claim that it's their software that got the Rift working. But if true, it feels like there should be some discrete evidence of that by looking at what's running on the Rift.
After reading, I was reminded of ConnectU LLC v. Mark Zuckerberg and The Facebook, Inc. Which, given recent events around the ownership of Oculus, is hilarious.
But directly using ZeniMax properties to promote the thing while working under a cloud of IP ownership uncertainty was probably not a great move.