I don't understand that as a criteria to be hired. I could see it as something to help show off, but shouldn't you as an employee be focusing on your company's codebase and not OSS products (unless there is some bug in the product you could fix that impacted your company)?

Maybe it's since I've always worked for companies with > 500 employees, but there is always a pile of work on the products I've worked on that there was little time to contribute externally.