Are alternative metrics taken seriously by hiring committies?
I served on a hiring committee in mathematics at a research university in the United States, and I don't believe that any of us paid attention to the sort of metrics you describe. 

My personal inclination is that I would not recommend listing any of this information unless it is unusually notable, e.g., if someone particularly well known blogged extensively about your work. However, different countries, universities, and departments might operate differently.