The gitdm scripts come from LWN who do a regular "who writes the kernel" report but can work on any git repo.

You can be fairly certain that patches coming from a corporate domain are paid for their time. You can add extra metadata to track people who use personal or org addresses if they confirm it's a paid gig. The project I work on most is about 75% paid contributors with hobbyists and academics making up the rest. The good unpaid contributors can often get hired if they want to be.