Ka'aihue, 27, began the season with the Royals but hit .195 with two homers in 23 games. He spent the rest of the year with Triple-A Omaha, batting .272 with 11 homers and 65 RBI in 95 games to help the club win the Pacific Coast League championship.
The Royals designated him for assignment September 21.
Hollingsworth, 24, spent most of the year at Double-A Midland, posting a 6-5 record and 3.61 earned run average in 17 games (16 starts). He struck out 66 and walked 23 in 94 2/3 innings.
The right-hander then made two starts for Triple-A Sacramento and gave up six runs in 10 2/3 innings.
To make room for Ka'aihue on the 40-man roster, the A's recalled pitcher Joey Devine and placed him on the 60-day disabled list with a right rhomboid strain.