Redditor Berdu has snapped images from a mod created by JJxORACLE for Grand Theft Auto 5, which replaces the ship's blimp with a Reaper from BioWare's Mass Effect series.
The full Imgur gallery of the images is available to view below, while higher resolution pictures can be found on Flickr.
The mod is currently in beta Blimp v1.01, but you can download the Reaper-adding content over on GTA 5 Mods. Any other ships you'd like to see hovering over the skies of Los Santos? An Imperial Star Destroyer would probably get my vote but sound off in the comments.