The Raiders' long snapper is Jon Condo. That is well established. He is a Pro Bowl player and has been the stalwart special teams pitcher for the Raiders for the past six seasons. But, there has to be a backup plan for every possibility, so they have brought back long snapper Nick Guess.
Last season the Raiders learned the hard way what it was like to suddenly lose Condo. He went down with a concussion in the team's season opener against the Chargers and disaster ensued. The Raiders lost that game due almost solely because of Condo's absence. They didn't have a real backup plan.
Technically, it was linebacker Travis Goethel who was pegged as the emergency long snapper but the team hadn't given him much of any practice. The result was a series of errant snaps that resulted in a fumble and a blocked punt and ultimately a loss.
In the week following that debacle, the team brought in long snapper Nick Guess and signed him to the practice squad. Guess was called up to the active roster in the event Condo didn't pass concussion tests, but Condo did pass those tests and Guess was not activated on game day.
Guess played long snapper for the University of Tennessee for 25 games beginning in his sophomore season. He spent time in camp with the Chargers prior to the 2012 season.
You can't say this staff doesn't learn from their mistakes. The special teams coordinator was fired following the season and now they have brought in Nick Guess even before OTA's just to make sure they are well-prepared.