Here's a quote from the press release:
Our decade-long partnership with Red Hat has always been focused on customer value and innovation. Today, we are extending this partnership to include cloud computing – broadening our reach and answering the strong customer demand for cloud computing services," said Maria Azua, vice president of Cloud Computing Enablement at IBM. "Red Hat Enterprise Virtualization is an optimal hypervisor technology for the infrastructure offerings on the IBM cloud."
Virtualization is one of the foundational technologies of cloud computing, so it's great to see that when it came to building its own cloud, IBM chose Red Hat Enterprise Virtualization as the optimal solution amongst all the available possibilities in the market.