The other day, I posted my interview with the creative director of "Dead Space 2," wherein I asked whether the similarities between Unitology and Scientology were intended. You can read the full answer right here, but the gist is that Visceral wasn't lampooning any specific religion, but rather organized religion in general. Considering Scientology's litigious history, it makes sense that EA and Visceral would be careful, but that doesn't make it any easier to ignore the similarities between the two religions.
If you're looking to delving deeper into the question of whether Unitology was based on Scientology, look no further than this excellent piece on Ars Technica, which provides screenshots and video to compare the two.
There's definitely some stuff I missed in there, including the "unification" connection, and a more detailed look at how the two ranking systems work. There's also that uncanny shot at the top of this post, which is pretty tough to ignore.
What's great about "Dead Space 2," though, is that you can ignore just about all of this backstory and enjoy the game as an excellent, science-fiction action-adventure. If you want to take the time and translate all of the Unitology script on the walls, or discover every audio log, you're likely to get more out of it, but either way, you come out on top. Just don't expect the game's events to make a ton of sense, as I've been through it twice and I'm still scratching my head over what exactly went down. Ah well, hopefully "Dead Space 3" will clear things up.