Yeah, I wouldn't. Even if it can be verified that I spent time on there, it's not an activity in which I could a) present any sort of tangible evidence of my progress or b) have a supervisor to vouch for the work I did. My main thing is just that it's not an official commitment which I signed up to participate in, and even though it may be useful to others, it doesn't fit in the standard idea of volunteering adcoms have expressed interest in. Of course, not all other volunteering activities are similarly verifiable; I draw the (perhaps arbitrary) line here, but I respect that everyone has a different line.