Real World article
(written from a Production point of view)

"Vegans" were a species only mentioned in the shooting script for The Motion Picture (dated 19 July 1978). The script briefly mentioned "high-domed Vegans" as an example of the aliens present in the Starfleet Headquarters scenes. [1]

Steven Lance's character was described as "an alien being from the planet Vega" in a publicity photo. [2] However, he was later identified as a Rhaandarite.