They may not sing but their popular tracks still have vocals don’t they?
Take a look at the story of Martha Wash, the huge iconic voice behind "everybody dance now", "ride on time" etc. You can't deny that these type of vocals are the tent-pole of those tracks but they basically scammed her by using demo sessions and using lip-syncers in music videos.
https://www.rollingstone.com/feature/martha-wash-the-most-fa...