Did Magilla Gorilla and Grape Ape ever meet up in any Hanna Barbara cartoon?
I’ll even take a guest appearance on Harvey Birdman, Attorney At Law. 
Both characters are in the 2021 cartoon series Jellystone!, though I’m not sure if they are ever in a scene together.
If comic books count, then they appear to have met at a special Laff-A-Lympics
An updated Laff-A-Lympics called the “Superstar Olympics” appeared in Hanna-Barbera Presents #6 in 1996. The Superstar Olympics featured Atom Ant, Augie Doggie and Doggie Daddy, Barney Rubble, Betty Rubble, Boo-Boo Bear, Chopper, Cindy Bear, Dick Dastardly, Fred Flintstone, Grape Ape, Hokey Wolf, Huckleberry Hound, Jabberjaw, Magilla Gorilla, Muttley, Peter Potamus, Pixie and Dixie and Mr. Jinks, Quick Draw McGraw, Ranger Smith, Secret Squirrel, Snagglepuss, Snooper and Blabber, Squiddly Diddly, Top Cat, Touché Turtle, Wally Gator, Wilma Flintstone, and Yogi Bear.
I know who’s been watching Planet Of The Apes !
Weren’t they both in Laff-a-lympics?
Just Grape Ape.