I've written up my process here: We have the same doubts as you have about using domain admin credentials for WMI Montioring.
However, it's the most reliable option for all WMI / Performance Counters that the sensors monitor.
It's called "Remote Probe" and can be installed on one, or a few, or all your machines in your network.
Vincent Hi, a great thanks to ERIC Drezet from CNRS who give me a simple working solution.
To troubleshoot, I added the PRTG WMI service monitor for the WMI Service itself with a 60 second interval.