I wonder if there is a living to be made by a native-English
speaker technical author contacting these Chinese and HK
companies and charging for tidying up their "english"?

The term is "Engrish", and NO, THERE IS NOT.

I've been trying "forever" to get several companies, native and foreign --
including National Semiconductor -- to pay me to edit their docuementation.
THEY WILL NOT. It is of less than zero concern to them. As long as they make
money, the quality of their user manuals, etc, does not matter.