Any situation where one would want to defeat an interlock and probe a transmitter's B+ supply can be replaced by advanced troubleshooting skills period.
The only time high voltage is necessary for component testing is when looking for hi potential insulation breakdown. This test can be facilitated using a hipot tester which is current limited.
Your example CK.... Your am transmitter has B+ on the rf amp but none on the modulator? Look and smell for burned parts, loose connections then check the modulation transformer primary with an ohm meter. If the transformer and associated wiring seems OK take a bench DC supply and short across the primary center to one plate terminal at a time. Turn the supply up until it draws enough current to simulate the average modulator plate draw and look for intermittant drops in current from an open. If the situation is reversed B+ on the modulators but none on the final substitute modulation reactor where I wrote modulation transformer above.
This is 2011. Any company who employs someone who does hot work exposes themselves to unnecessary financial risk. This is especially true where work arounds are well known. Even a website like this could be a target of a lawsuit if some yahoo gets fried. You guys do give some good advice on occasion but dropping the "I used to be a broadcast guy" and advising someone to measure dangerous voltages is a a really bad idea IMHO. Sorry for my tone but I had one friend who is disabled due to a hot work accident. He was lucky. Another guy I used to talk with was electrocuted while measuring the B+ in his newly built Heathkit 3-500 amp. I'm sure VA3ES remembers him too. Think of the horror and danger to family members who have to deal with the aftermath of such accidents.
For builders unknown transformers can be checked by powering with a filament transformer and scaling the readings up. If you cannot apply the formula for cap input or choke input and come up with decent accuracy for the voltage in a new circuit it is time to put down the tools and hit the books.
The horror stories you tell of deal with people who did not have the background to safely work on this equipment. When a commercial TX goes off the air, I don't want someone who is unable to dive in and find the problem to spend the afternoon trying to figure out the problem because they won't take the internal measurements or a live visual inspection to confirm it. Ever try and find one of those internal arcs that does not leave an obvious carbon trail? Without question, sometimes the best way is to defeat those interlocks, shut the lights off and watch for the arc. Not a job for the faint of heart or the experience to do it in a risk free manner. But then again, you won't find anyone like that employed in this position. I mean no disrespect here either. This is a job you cannot be afraid of. Fear must be converted into knowledgeable respect to be successful here.