Dipoto said Jackson will take the final spot in the Mariners' bullpen, meaning right-handed candidates Donn Roach, Blake Parker and Mayckol Guaipe will open the year with Triple-A Tacoma.
The Mariners' seven-man bullpen will consist of closer Steve Cishek and fellow right-handers Joaquin Benoit, Tony Zych, Joel Peralta and Vincent, along with lefties Vidal Nuno and Mike Montgomery.
Vincent joined the Mariners immediately on Wednesday, having to just walk across the Peoria Sports Complex the team shares with the Padres, but Dipoto said he wouldn't be asked to pitch in the afternoon's game against his former team.