...according to this fansite: http://theavettbrothers.groupee.com/
Their official website nor their myspace confirm them as playing Sasquatch!, but it is feasible as they will be in Arizona with the Dave Matthews Band on May 6th. However, I doubt Dave Matthews will be at Sasquatch! as they always play three nights at the Gorge at the end of the summer.
If you can confirm or deny that the Avett Brothers are playing Sasquatch! let me know!