I think it's a slippery slope to assume that just because someone is involved in a community that they are necessarily a good employee, and conversely, if they don't involve themselves, that somehow deems them "not passionate enough" or not as talented.
Just anecdotally, I have a friend who has a wife and two kids. He's not going to spend all his free time forking on Github. He does take on side projects, and is a very talented developer. Sometimes peoples' priorities are simply different, but it's hardly a reliable metric to look at. And I say this as someone who does see himself as an involved member of the community.
I'm not saying you assume someone who doesn't have open source work / contributions isn't necessarily a going to be a good employee. I'm just saying it's materially harder to tell in comparison to someone with the same resume and a publicly-viewable history of contributions. Any time you have a choice between the unknown and known, it's going to favor the latter.
Just anecdotally, I have a friend who has a wife and two kids. He's not going to spend all his free time forking on Github. He does take on side projects, and is a very talented developer. Sometimes peoples' priorities are simply different, but it's hardly a reliable metric to look at. And I say this as someone who does see himself as an involved member of the community.