I'm pretty interested in more details about how this works.
Paraphrasing, the article claims that the chip is connected to the little management processor on the server (not the CPU) and that it can somehow call home to load malicious software onto the server itself... If you can do that, then I think you've pretty thoroughly penetrated the target network.
Most server boards have out-of-band management, meaning an extra dedicated network interface that is completely independent of the main OS and CPU. It's typically used to monitor things like internal temperatures, voltages, etc., but can also be used to remotely control the host server as if you were in front of it (send keyboard and mouse commands and see what would be on a monitor).
From what I understand in the Bloomberg article, this was their target. If you compromise that, you essentially have full access to the entire server as if you were standing in front of it.