Jinny, axolotls are not common in the wild because of habitat destruction, not the animals that live with them (except introduced species such as pike and largemouth bass). In the wild, they'd be surrounded by snails, small fish, invertebrates, whatnot.
The reason it is not recommended to mix these species in captivity is due to size restraints. If you had an aquarium the size of a room, and it was adequately set up with hiding spaces and such, it would be more than acceptable to create a natural habitat.