It is true that the culture of OSS contributions and IRC lurkers is a very small subset of the available talent pool. On the other hand, jobs that hire based on open source contributions are still a very small subset of the total available jobs. The vast majority of my friends in college were hired with little experience into large corporations, who are better equipped to have a smooth onboarding experience and on-site training.

FWIW, I contributed to an open-source project and was then hired to work on it full-time, and it has been a great experience.