I wouldn't consider it moot, but I wouldn't necessarily deduct points either. Open-source contribution is a good bonus in a developer; it shows that they have been able to cooperate others (among a group of people that are often unpleasant, ornery, or crotchety) and adhere to the requirements of the BFDLs, which shows adaptability. The big benefit of course if that you can go back and look up their interactions and the code they submitted and how they went about the whole thing, which is definitely useful in determining if the person would be a good hire. It also demonstrates a level of conscientiousness about their place in the community.

So, all that said, there are good reasons a developer may not have many open-source contributions, as you stated. So while I don't think it's good to necessarily detract from developers without that, I wouldn't exactly consider it moot, either; open-source dev is a very useful reference and a good demonstration of the candidate. If you can't contribute, you will miss out on some of those good vibe points, but that's the way things go sometimes I guess.