Ruffin posted a combined 3-3 record with a 2.09 ERA in 31 games with Double-A Erie and eight games with Triple-A Toledo.
Tigers Manager Jim Leyland said he knew little about his new reliever, who will be joining the team for its next series in Chicago.
"I know nothing about him," Leyland said, "other than he's tough, he's good and he's from Texas."
The 6-foot, 185-pound right-hander is just 22 years old. He was drafted in the supplemental first round (48th overall) of the 2010 First-Year Player Draft.
Ruffin is the son of former Major League pitcher Bruce Ruffin, who pitched for the Philadelphia Phillies, Milwaukee Brewers and Colorado Rockies from 1986-1997.
Oliveros pitched in nine games for the Tigers this season, posting a 0-0 record with an ERA of 5.63 in eight innings of work.