Although Dapper Jack's photos show him to be a dead ringer for Shaggy, there is no visible proof of what his dog Atlas looks like. The flashbacks showing Atlas are just the characters' imagination picturing him as Scooby-Doo.
A typing font called El Kabong is part of the plot. El Kabong was a Zorro-like alter ego assumed by Hanna Barbera's inept Wild West hero Quick Draw McGraw.