I think a case could be made that Dr. Fright, the villain of this Super Friends short from 1977, might have been an analogue for Batman's enemy, the Scarecrow, who'd make his H-B debut a year later in the Challenge series. Fright also used fear gas, but needed no costume. He was your garden variety misguided scientist of the period, and was never heard from again.
I should note that the Scarecrow would show up in the comic book version of the series during the winter of 1980. The only other Legion of Doom members to do so were Riddler & Cheetah (issues 1-2, pre-Challenge) and Gorilla Grodd (1979).