Nope, Munchlax first appeared in Pokemon XD Gale of Darkness, then was later discovered in the Pokemon movie with Deoxys and Raquaza.
Then we see it in the anime, where May also catches it in the episode, Berry, Berry interesting.
Then was later "seen" in Pokemon mystery dungeon: Blue rescue team and red rescue team.
And again in Pokemon mystery dungeon: Explorers of Time/Darkness.