There are no printed credits to this film, other than the name of the songwriter and the studio that made it.
This cartoon became an annual tradition on Chicago TV station WGN-TV. It was first shown there on 18 December 1956 and is still shown there, though not on Bozo the Clown (1959), which has since gone off the air. The date on which it made its debut on WGN occasionally causes confusion over the date that this cartoon was made; some web sources list it as being made in 1956, but this is incorrect.
This cartoon is shown on WJAC-TV in Johnstown, Pennsylvania. It's one of three shorts from that era that have been shown continually on that station (now an NBC affiliate) since the 1950s. The others are Suzy Snowflake (1951) and Frosty the Snowman (1951). Like "Hardrock", Suzy Snowflake was produced by Centaur Productions; "Frosty" was produced by UPA.
Frazier Thomas, of Garfield Goose and Friends (1952) fame, was always asked where someone could find a copy of the song 'Hardrock, Coco and Joe'. He only knew of the cartoon. So he requested to have the song made into a record. The Les Tucker Singers then recorded the song, and it can be found on a 45 rpm record. Other groups have since recorded their versions of the song.