This is real, official art to promote a Fallout game. I found it on the site of the artist, link here.. The artist also did art for a promotional pinup calendar for Brotherhood Of Steel, but I noticed with a chuckle that on his resume PDF he says it was art for Fallout 2.
Yeah a guess youre right, a lot of cover art of the era has a similar composition. The ghouls about to chuck green radiation balls really reminded me of the imps in Doom.