Did we read the same page? When you buy Novell (SUSE) support for RedHat EL, you will still run your original RedHat EL installation but then update packages rebuilt by Novell. Technically that's the same like adding the CentOS repo config to your RedHat installation and then install all updates from CentOS instead of RedHat. What a mess, why would anyone in the world want this? And then pay $ for the mess...
Most likely because of relative cost and/or perceived value of SLES vs RHEL?
Novell is essentially offering to help you while you switch existing kit over to SLES. If you're already paying for a RHEL subscription, Novell's offer may have a lower cost or offer better value then RHEL