"Aaron was the one guy that it was really tough to know how to use," manager Don Mattingly said before Saturday's game against the Pirates.
The Dodgers still have an excess of rotation-worthy pitchers, though. Left-hander Chris Capuano, who made 33 starts for the club last year, remains in the bullpen. Lefty Ted Lilly is on the disabled list and began a Minor League rehab assignment on Friday with Class A Rancho Cucamonga.
Hernandez, 36, is in his 15th season in the big leagues. The veteran catcher has a career .264 average and was an All-Star with Oakland in 2003. He was designated for assignment after Spring Training.
"Ramon gives us invaluable veteran experience and additional leadership at the catching position," said Dodgers general manager Ned Colletti. "He's worked with great pitching staffs in the past, and we feel he will provide solid contributions to our pitchers and be a great resource for A.J. [Ellis]."
The Dodgers now have three catchers: Ellis, Hernandez and rookie Tim Federowicz.
How long will the club carry three catchers on the active roster?
"We're not going to do it for an extended period of time," Mattingly said.
The Dodgers will need to make a roster move on Wednesday, as the club expects to activate right-hander Chad Billingsley from the disabled list to start at San Diego. Federowicz, who is scheduled to make his first start of the season in Sunday's series finale against Pittsburgh, appears the likely candidate to be optioned to the Minors.
According to multiple reports, the Dodgers are sending the Rockies $4.25 million. Harang is owed $7 million this year with a $2 million buyout for 2014. Hernandez is owed $3.2 million this season.
Austin Laymance is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.