If it were an employer's market you could probably get away with that.

Why would an employer want to do that?

A github account just makes it slightly more likely that the candidate's experience involves more open source, and less proprietary code.

Personally, I'd rather filter candidates based on factors that relate to their performance. After all, bad hires are very expensive... as such, most of these shortcuts strike me as incredibly misguided nonsense.

Because they can see first hand the quality of the code (plus all the other meta information that comes along with commit logs). How do you evaluate proprietary code at anywhere near that same level?