You have more than one issue. First, something makes vzctl pull in the RHEL/CentOS/SL 6 kernel as a dependency. This shouldn't happen on CentOS 5.
You should only be getting kernels from the openvz-kernel-rhel5 repository and not from openvz-kernel-rhel6.
So, double check if your openvz yum configuration is properly set for RHEL/CentOS/SL 5 and not 6.
Then manually specify the arch when installing the kernel. Assuming you want the 64-bit kernel and tools:
yum install ovzkernel.x86_64 vzctl.x86_64