I am thinking that it is not as important whether we detect the same CPU % as the OS. It is more important to know whether a regular Java thread in the VM is being resumed more or less often.
If we answer the following question positively, then we have a reason for serious doubt:
"Did the monitoring thread reach a point where it's being resumed 10 times less often within the last 15 minutes time slice than it was in any period of 15 minutes since the VM started?"
Of course these numbers are arbitrary and should be possible to configure per deployment.

Ivelin