Production testing of circuit breakers that I am familiar with 1200A-3000A uses a ductor or micro-ohm meter. It circulates 100A for the reading. This is much less than the 63KA short circuit amps it is guaranteed to interrupt.
And the 100 amps is less that the 3000-30,000 amps a circuit breaker is exposed to, but it gives us a reading for reference. With the DLRO you would take comparison reading along the length of the busway and across each coupling.
Will the megger readings mean anything, YES it means if you know what you are doing you will minimize the risk turning the busway into scrap.
I have NEVER had a busway I tested blow up, I have been on countless jobs were the busway was energized without testing. I was there to install temporary and discern what caused the busway to fault.
Usually water and/or bad installs.
The number one blow up we see is busway, followed by bolted pressure switches and EGC fished into energized switchboards with the other end connected.