Sometimes it happens that the cpu and memory usage of individual ESXi 5.0 hosts will not be available in the vCenter:
Solution (respectivaly a workaround):
In this case a restart of the management agents will help to solve the problem.
Just login to the console and press F2 “Customize System/View Logs” to switch to “System Customizaton”:
Now select “Troubleshooting Options” and then “Restart Management Agents”:
It lasts about a minute till the data will be presented in the vCenter as usual.