Yeah, Halo and Ringworld have as much to do with one another as Ringworld and Lord of the Rings. Yeah, they all got rings in em, but they're not the same rings. For one thing, the Halo object is absurdly small...its in orbit around a friggen gas giant, for crying out loud! The Niven Ringworld is easily the size of 6 billion earths, stretched into a long ring around a SUN. You could set a game on a fraction of that surface and never run outta room.
Also, to be frank, I didn't think revelation space when I played Mass Effect...I thought Mass Effect when I played Mass Effect. While they have plenty of tropes and references, they still bind it into a coherent and (in my opinion) fucking awesome universe.
This isn't an isolated phenomena.
Even my all time most favorite game of all time, Homeworld, borrows liberally from Battlestar Galactica, Star Wars, and the Old Testament. Of course, Homeworld was originally meant to be a BSG game.
For another more recent example, lets take the tabletop RPG Eclipse Phase. Eclipse Phase is what happens when you take Altered Carbon, Chasm City, The Uplift Series, Transmetropolitan, Terminator and Stargate and put them all in a blender then set it to FUCK AWESOME.
(Seriously, buy Eclipse Phase right now)
Earlier, someone mentioned Babylon 5...the author of that show freely admitted to stealing a bunch of his ideas from various sources outright. To quote him: "Bad writers borrow. Good writers steal."