From Season 2 of The New Scooby-Doo Movies:
One of the cool things about the series was putting the celebrity guests in unlikely positions. In "The Spirited Spooked Sports Show", Tim Conway (The Carol Burnett Show) swaps Hollywood for coaching, with predictable results. Casey Kasem (Shaggy), who usually essayed extra, mostly generic, parts in every cartoon he did early in his career, voices the track announcer in the hilarious final scene.
Ya know, it might've been cooler if they'd gotten Carol Burnett to guest star, and maybe they did send a feeler her way. After all, another of her repertory company, the late Harvey Korman, had worked for Hanna-Barbera in the 60's (he was Gazoo on The Flintstones) before joining Carol. Oh, what might've been.