It is best to assume that either they will go for the gills or that they will be a snack. Some people report long term success housing axolotls and fish together, but most experts agree that housing them together is not a good idea unless you intend the fish to be lunch (and they aren't gill nippers).
In addition to them snacking on each other, most tetras in the fish trade like warmer water than axolotls do. So, one or the other would be living in unsuitable conditions.
Some "tropical" fish do tolerate (and even prefer) cooler conditions (white cloud mountain fish). But they still are likely to become snacks.