I had a similar issue on a Dell Chassis.
I found if you turned off the power management/profile in the BIOS (set it to performance as opposed to performance/watt) I no longer had this problem.
Not sure you actually need to do this...some research on the bios/server power management (in the optimize for perf per watt mode it was in) say that it should not effect performance significantly as it should feed power to the CPU as it needs it. But it does seem to lag enough that the VMware chart is effected.
Found the answer here:
In my experience this can be caused by problems with your vSphere HA configuration. Make sure all your hosts are connected to the HA master. If a host is not connected to the HA master, or isolated, it's resources will not be counted in the VROPS workload calculation and will likely trigger workload alarms.