A much better question
> make sure you ask the question: "How many developers do you have submitting code ...
Nah! Code is easy, code is "fun". You don't have to pay hobbyists to write code: they do it for free.
Documentation is boring. Documentation is dull. Documentation is hrad 2 get wright.
Testing is even worse.
Project management is next to impossible.
So if companies want to contribute to OSS, the best thing for the community and its users would be to leave the code to the geeks who like doing it and to add far more value by testing the stuff they produce, using it, managing the change control and writing books, articles, man pages, wikis, examples (preferably working examples) and FAQs. Those are the things that are missing from most projects - and are the biggest impediments to the take-up of "free" (free as in no cost: so long as you put zero value on the hours or days it can take to wrangle some of this stuff into working shape - or realise it's irredeemable crap and you've just wasted a week on it).
That's where the biggest contributions will come from. Even though those contributors won't get the recognition and kudos. That's why companies are in the best position to donate those efforts.