The mines the dogs are excavating in the pilot movie used to be the city of Townesville from the The Powerpuff Girls (1998). This is evident from a billboard which has a picture of the Talking Dog which appeared in an episode of the "Powerpuff Girls".
In Episode VIII, one of the bounty hunters in the woods that is riding a robotic elephant is a character from "Dial M for Monkey" from "Dexter's Laboratory." "Dexter's Laboratory" is also created by Genndy Tartakovsky.
Tartakovsky has acknowledged taking some of his inspiration from the Frank Miller graphic novel Ronin, including the premise of a master-less samurai warrior thrown into a dystopic future ahead of our present.