Perhaps I misunderstood. But isn't Github help you filter out such candidates, is it? They have some big projects, but their contribution calandar should be almost empty, cuz all the code is pushed into Github at once.
I would also check they PR, issue and comments, to get some idea about how they work with stranger; what are important to them when they suggest ideas, contribute to existing code base; how they reply to critic or question from project owner, etc.
Also, just my opinion, most of us - software developers - can't live without OSS. We should contribute back when we could. That's why I usually prefer resume with a non empty Github profile than the others.