The release of vSphere 5.1 introduces support for the Unbreakable Enterprise Kernel on ESXi 5.1, with the following support considerations:

• The Unbreakable Enterprise Kernel includes select drivers for VMware paravirtual devices.
• Prebuilt kernel modules are not included in VMware tools for Unbreakable Enterprise Kernels in ESXi 5.1.

For more information about software support, please check the VMware Compatibility Guide