Again, exactly correct. I've been experimenting with NCVT (Non Contact Voltage Testers) such as the Fluke VoltAlert (Standard 90 to 1,000 volt model) for use in identifying hot-chassis conditions in the situations you describe. Here's a video of how me testing a 40 ft RV trailer that's had its chassis electrified with a variable AC bias from 40 to 120 volts: Hot Skin RV proximity test full scale - YouTube This simple NCVT check on microphones and backline stage amps will find anything biased with 40 volts or more AC above the earth plane.If a powered piece of equipment malfunctions with the hot connecting to chassis there is no return path through the ground wire to trip the breaker, thus the chassis remains electrified. This obviously is potentially deadly to anyone that touches the malfunctioning component. The component may still work fine with a hot chassis.
If this happens to be a genny gig and the genny doesn't have continuity with the ground due to its rubber tires and the trailer tongue is insulated from the ground in some fashion, the electrified chassis may not shock the person touching it. But don't worry - you can still die - what is required is completing the circuit with your body by touching the hot chassis and another component with an issue.
If your genny isn't properly G-N bonded/earthed via a ground rod, and a hot-to-chassis short in a piece of stage gear electrifies your stage ground plane, this $20 tester will scream at you when it gets within a foot of anything large connected to a grounded power plug (like a mixing console or guitar amp) and within a few inches of any microphone or guitar on stage. And it will certainly scream at you if you get it within a foot of the genny itself that isn't properly earthed via a ground rod and "floating" above the earth plane. Proper genny grounding and bonding is very important to the safety of both your crew and gear as well as the performers themselves.
See No Shock Zone for a bunch of articles I've written about basic electrical principals. Some of these are quite basic, but for those who need a review of what voltage and amperage and wattage really means, this is a good primer. I also have bunch of YouTube videos at howtoseminars - YouTube that shows how to use test gear such as DMM's, clamp meters, why extension cords overheat and other cool stuff.
FYI: I have all of the major Ground Impedance Testers on my bench - Amprobe INSP-3, Ideal SureTest, and Extech CT-70 along with an "antique" Woodbridge GLIT I bought back in the late 70's with I first got my Master Electrician License, and plan on a comparison article pretty soon. I'll keep you posted.