This will be Pollock's fifth stint in the big leagues this year. He filled in twice for players on paternity leave, served as the 26th man for a day-night doubleheader and also was up in April when outfielder Chris Young injured his shoulder.
Pollock hit .250 in those stints, as well as hitting .318 for Reno.
Jacobs returns to the big leagues for the first time since 2010, when he made 28 plate appearances for the Mets. The 31-year-old's best season was in 2008, when he hit 38 homers and drove in 93 runs for the Marlins.
Jacobs was suspended for 50 games last year after testing positive for human growth hormone. At the time, he was with the Rockies' Triple-A affiliate.
Jacobs hit .279 with 18 homers and 60 RBIs for Reno this season and served as a mentor for some of the team's younger players.
"I'm grateful for the opportunity," Jacobs said. "It's been a long time. It just feels good, it feels really good. I'm excited about it."
The D-backs would like to bring Jacobs back in 2013, but will face a 40-man roster crunch this offseason.
"We've got some kids that we've got to add onto the roster, and we've got some guys on the 60-day [disabled list], but I think it's a need," Towers said of the left-handed power Jacobs offers. "We've got Ryan Wheeler, but it'd be nice to have another left-handed power bat. I think he has interest in staying in the organization. We'll see what happens."