How nazi is IBM when it comes to intellectual property? That will probably determine the likeliness of them axing CentOS, Fedora etc as they can just say it impedes on their IP. A big corporation like IBM is probably not going to care about the GPL or if it goes against it.
Doesn't matter, really. As mentioned before: free RHEL-compatible alternative is important for the ecosystem, i.e. testing, cloud, factory-built VMs etc. CentOS has to survive.
Just a simple example of CentOS importance:
When you download a VM-packed software distribution (often learning or developer versions), they'll usually be based on CentOS. That's because every "enterprise" software for Linux is built with RHEL in mind.
If CentOS vanishes or isn't free anymore, this whole idea dies.
Also, don't think IBM is some evil corporation that wants to kill all free software. They're a huge contributor to open-source and they've given us quite a lot of things.
Sure, IBM used to be very close to consumers, so we "felt" their importance. Today they're focused on enterprise solutions, but they remained a similar company as they used to be.