There is a very large corpus of FLOSS software out there serving everything from individual itches to whole industries. Any project that is important to someone's bottom line is likely to have paid developers working on it but often alongside hobbyists.

The project I predominately work on is about 90% paid developers but from lots of different companies and organisations. Practically though the developers don't care about the affiliation of the other developers they work with but the ideas and patches they bring to the project.