No, as far as I know, at Apple, this is strict - you cannot contribute to OSS, period. Not from your own equipment nor your friend's, not even during a vacation. It may cost you your job. Of course, it's not universal for every team, but on teams I know a few people - that's what I heard. Some companies just don't give a single fuck of what you want or need, or where your ideals lie.

I suspect it's not just Apple, I have "lost" so many good GitHub friends - incredible artisans and contributors, they've gotten well-payed jobs and then suddenly... not a single green dot on the wall since. That's sad. I hope they're getting paid more than enough.