There is a big difference from being paid in USD and being paid in the equivalent of USD in Yuan. Ever try to get 1 million USD equivalent of Yuan out of China before?
If these engineers are Chinese (which they are) and live in China they don't need to get it out of China.
You could say the same about people living in Venezuela, Ukraine and Russia. I would assume most (at least as a store of value) would prefer not to hold their local currency.