This person appears to be Declan Mulholland, the stand-in from the deleted scene in which Jabba the Hutt was meant to appear:
Mulholland would have been replaced with a stop-motion creature during post-production had the scene not ended up on the cutting room floor. - source
The look for the stand-in was never canon; Jabba was never going to look like the that. Why does his face appear on the official Radio Drama cover if he was just standing-in for where Jabba was meant to appear?
In the Radio Drama, Jabba's lines from spaceport scene in A New Hope were kept but given to a humanoid character named "Heater" — this is described, for instance, in A Brief Guide to Star Wars by Brian J. Robb. For the cover artwork, Mulholland's likeness was used, given that he was the human giving those same lines in the unused footage.
Heater also appeared in Star Wars: The Essential Guide to Characters. The Essential Guide sketch reaffirmed Heater's look as being that of Declan Mulholland from his stand-in portrayal of Jabba.
In short, "Heater" was a retcon name given to Declan Mulholland's "Jabba", and this became part of the Radio Drama. The cover reflects this.
This interview with Randy Martinez, the picture's illustrator has confirmed that the character depicted is "Heater", a high-ranking henchman of Jabba the Hutt.
The character on the right with the crazy hair is Heater. No, that’s his name… Heater. Truth be told, he was Jabba in the original script. They actually shot these Jabba scenes with the actor who depicted in my painting. Several years later, Lucasfilm reinserted the confrontation scene Han Solo has with Jabba the Hutt outside of the Millenium Falcon, but put a CG Jabba the Hut over the actor who portrayed Jabba in the original filming.
By 1981, when the Radio Drama was produced, Lucasfilm had already started developing Jabba the Hutt for Return of the Jedi. As we all know Jabba is a big slimy slug-like Hutt, and does not speak English. To patch this continuity problem, Lucasfilm changed the name of the Jabba character to Heater for the Radio Drama. But then, in the movies he went back to being Jabba the Hutt for the Special Edition… I know it’s confusing, but Heater, for all intents and purposes, is Jabba the Hutt.
