Ultrasonic cleaning is an industry unto itself and i know very little about the details of what it can or can't do and how to do it.
I've used it on various small parts, like carb parts, of different sorts and sometimes they come out shiny clean and sometimes not.
The rusty chain was just a experiment with an unexpectedly good result.
But after reading a bit on the net, it turns out that removing insoluble junk (like rust?) from a hard surface (like steel?) is one of ultrasonic cleaning's specialty.