Hybrid Kernel is CloudLinux 6 (2.6.32-lve1.x) kernel compiled for CloudLinux 5 OS. It brings new features available in CloudLinux 6 kernel, like IO limits, to CloudLinux 5 servers. When you switch to the hybrid kernel, you will also switch to a new channel, that has all other components compatible with the new kernel. The kernel is as stable as the CloudLinux 6 production kernel and has the same features.
While the kernel itself is fully production quality, the process of switching to Hybrid kernel is not perfect. This is mostly due to differences in naming for the devices and modules between 2.6.32 and 2.6.18 kernels. As the result, your server might not boot with the new kernel. To solve that, boot into previous (CL5) kernel, and convert back. After that - notify our support department by creating a ticket. In most cases, we can resolve all the naming issues, and make sure you can boot into Hybrid kernel.
Switching to Hybrid kernel:
# yum update rhn-setup # /usr/sbin/normal-to-hybrid # reboot
To convert back to original CloudLinux 5 kernel:
# yum update rhn-setup # /usr/sbin/hybrid-to-normal # reboot