"Right now, they are both [in the rotation] for us, but there is a lot of time before Opening Day," Dipoto said. "One thing we like about Santiago is his versatility, as he's had some success in the pen."
Skaggs, a 22-year-old lefty from Santa Monica, Calif., is a former first-round pick of the Angels who was traded in 2010 to acquire Dan Haren. Skaggs spent most of last season at Triple-A and went 2-3 with a 5.12 ERA in seven starts for the Diamondbacks.
This is the second time that Dipoto, who formerly worked for the Diamondbacks, has traded for Skaggs.
"He's 22 and athletic with a three-pitch mix," Dipoto said. "Like a lot of guys who debuted so young, he's just cutting his teeth in the majors, and we believe in his upside."
ESPNChicago.com's Doug Padilla and The Associated Press contributed to this report.