How do I disable "Processor Power and Utilization Monitoring" on an HP ProLiant server?

This is outlined in the document you linked under the "Tuning Procedures" heading.

In order to enter the Advanced system options menu for modifying a G6 or newer HP ProLiant for a low-latency application, you need to get to the main BIOS screen by pressing F9 during POST.

Once there, type Ctrl-A. This will present an additional menu named "Service Options" at the bottom of the list.

Select "Service Options" and you'll see the advanced system options, including the optimization you're looking to make. Change "Processor Power and Utilization Monitoring" to "Disabled". Escape and follow the prompts to save your changes.

One note. In realtime applications, there are a good number of things than can be tuned before resorting to this, but the setting is safe.