It makes the CPU work indeed...
yum-updatesd takes up 100% CPU all the time. Thought the proces has a low thread since it gives away CPU resource if other processes need it.
But if you set your bios to overclock, yum would indeed try to use 100% at the overclock rate you chose. In this light, you need to watch out when overclocking a processor when using yum. It may indeed smoke your CPU! Make sure you know what you are doing when overclocking!
But that's what you always need to do so don't blame yum