An open G chord is technically third position given its location of the root note, but in RockBand3, that particular variant displays a "2" that falls on the A string.
We've gone into thorough detail about how pro guitar works on the software side of RockBand3, for better and for worse (you can check out that impressions piece here), so for this review we're largely going to focus on how the hardware feels.
In fact, if you want to take advantage of the drum kit, guitar and microphone in the hot-selling Xbox 360, PlayStation 2, and PlayStation 3 title "Rock Band" it helps to have more than a few friends.