Yes, that really is Janet Varney (Korra) singing this song. I just HAD to make a video of Korra, herself, (And Kit Pongetti as Asami) singing it!
Dun dun DUNNNNNNNNNN! (Yes, I’m the one who made this)
I would just like to point out Feathered Hat Guy’s more subtle appearance in episode 1x08 today. Bigger version: http://i.imgur.com/M0Dau.jpg