I'm not sure why it has been such a hot topic suddenly, but people are all atwitter on the Twitter about using GitHub as a measure of software developer awesomeness in the context of hiring. (Perhaps it's because Microsoft just bought GitHub, which has generated a lot of emotional reactions reminiscent of 1999.) Some people insist that this is an important thing to look at.
My take is that it is important, it's just not the only thing. If you just anecdotally look at various profiles, including my own, you'll see a very spread out and inconsistent graph of contributions. I'm at 69 as of this moment, and 19 of those are just in the last month, when I've had unanticipated free time. I also haven't been a full-time heads-down developer since a short contract in 2013. So what does that graph really tell you about me? Now consider someone who works for a bank or in defense. It's not likely that anything they do in their day job will end up online, and they may even be prohibited from contributing to open source as part of their job. Does that make them substandard developers? Of course not.
Of course, I love to see developers to contribute to open source, but you'd have to be a little crazy to overlook someone because they haven't, or can't (or simply don't have time) contribute. There are a lot of reasons not to disqualify people, but many reasons as a whole to let someone pass deeper into your hiring funnel.
There's one other disqualifier that bothers me, and it's not limited to my industry. Sometimes people set up abstract scenarios or role playing in an interview, with the intention of finding a specific "right" answer. This is dangerous, in part because abstract and contrived situations can't possibly result in real life interactions, but worse, if you're looking for specific answers to abstract situations, what you're saying is that you're not interested in people who may bring something new and different to your organization. Few things can cause atrophy like hiring clones. The world and your business will change whether you want it to or not, and not bringing new ideas by way of new people can result in a lack of self-awareness.
The bottom line is that there is no silver bullet that can predict who is best for your team, or what is indicative of success. You can't distill it to one thing, so you have to consider many things. A GitHub profile is just one of many things to consider.