Hu, who pitched the ninth for the Rays on Thursday, has been used as a starter at Durham. Cash said Hu will now be used as a reliever so he can learn that role.
"Which I think will be a good thing for him and us," Cash said.
Cash said Marks "seemed like a guy who would be the right fit."
"Let's see how the game plays out," Cash said. "He's a guy who came up last year. Pretty impressed the way he reacted on the mound. He didn't seem to get too amped up. He was the same guy. So excited to have him here."
Marks was 4-1 with a 4.60 ERA in nine appearances for the Bulls, including one start.
The Rays selected Hu on Thursday when Erasmo Ramirez went on the paternity list.
"The baby was born this morning," Cash said. "I'll talk to Erasmo, give him some time to catch up on his sleep, then give him a call after batting practice."
Ramirez had a son.
Outfielder Shane Peterson cleared waivers and has accepted his outright assignment to Durham. He is scheduled to report on Monday.
Peterson hit .263 with a home run and six RBIs in 14 games for the Rays this season.
Bill Chastain has covered the Rays for MLB.com since 2005. This story was not subject to the approval of Major League Baseball or its clubs.