When I was at google they said "we have a standard contract we'll most of the time be happy to sign that says we claim no interest in your outside project. Submit your project here and we'll get back to you ASAP".

They often put out memos about the types of things that were not okay and later when they were ok. For example then they were exploring games in google plus back during the Farmville crazy they said "Sorry but for the time being no games please .. unless of course you want to make open source demo games for our APIs/Platforms". A year or so later they said "okay, games are fine now so feel free to submit to get your contract signed"

The best thing about that is there's no ambiguity because you have a contract for your project. Github's policy is awesome but you're still at their mercy if you thought your side project was unrelated but they happen to think it is. In fact the larger any company gets the more likely you don't know all the things being worked on. A contract for your side project clears that up.