I worked with a firm that did this. Basically, they had one project manager who could speak decent English and about six developers who couldn't. The English-speaking PM was on calls with us, and then he'd farm out the work to the developers.
It was a win-win, because their group was getting work, and we were getting decent results at a discounted rate compared with on-shore resources.
But it's pretty clear that anyone looking for fake interview candidates is not actually planning to do that. They're essentially counting on the fact that it takes many companies a little while to get rid of a bad hire.