It’s not really a “hacker portal”. It’s an alternative frontend. In the software industry, a frontend is the part of a piece of software that the user interacts with, so Nitter is just a frontend that interfaces with Twitter’s backend (the part of a piece of software that the user doesn’t see). Of course, this is an oversimplification, but this has nothing to do with hacking or anything of the sort. It’s just an alternative UI for Twitter.