Hi kinkyoto,
As Blaze wrote, feeder fish (guppies, mountain minnows, cardinal fish) are fine as long as you follow a strict quarantine before giving them to your axolotls.
Neons are not suitable for an axolotl tank, though, because as tropical fish, they require much warmer temps than the axolotl. They would be suffering in the cold axolotl tank, and it might take awhile for a lazy axolot to get around to eating the fish. Even if the fish is "just food", it is still a living creature and should not be subjected to torture before death. The fish I mentioned above are good, though, particularly guppies as guppies are prolific breeders and soon you will have a constant supply of them.
-Eva