Not quite, the videos are recorded long before they're uploaded to youtube
But in a sense it's kind of live, the audio commentary is done during the capturing of the in-game video.
Look up ChuggaConroy, Josh Jepson, Proton John, and NintendoCapriSun on youtube, they're all very good and entertaining let's players that I know about.
A blind run basically means that I've never played before and have no practice whatsoever. It usually results in a longer let's play but more interesting commentary as a result. At least that's what I am hoping for