No ventilation hole. That was one of the things I wanted shug and cavediver to determine - whether a vent hole was necessary with the breathability of this fabric. The way shug is using it, apparently not. I still like a sock better than a topcover, but for a lightweight option, it does the job of keeping in a little extra heat.
The extra weight difference between your SS overcover and this is probably from the ggr end tabs and shockcord/cordlocks. I really have to work hard to think like a gram weenie. I've never seen a SS overcover, so it would be interesting to see how they compare.