They are a completely different species.
They're not a listed species, but like axolotls, their native range is extremely limited and threatened by human development. By definition of the word, yes, they're endangered. But unlike axolotls, they currently have little legal protection.
The differences between the species are minimal. They only diverged as two separate species because of geographic isolation, much like all the other neotenic salamanders of Mexico (there are a dozen, give or take).
They can interbreed, but I cannot more strongly recommend NOT cross-breeding them. Unlike axolotls, Ambystoma andersoni genetics are relatively pure and unadulterated. Interbreeding them will just muddy up the gene pool and create problems in the future in regards to possible re-release programs (no matter how slim).
The hybrid would probably be fertile, causing further problems. There's a scientific principle called the Hybrid Vigor theory, where the hybrid between two species is actually larger and stronger than either parent species, and is therefore able to outcompete them for resources. This is why all ambystomatids are illegal in California; the Federally protected California Tiger Salamander resides there, and by preventing all other ambystomatids from coming into the state, they're trying to keep it's genetics pure and remove the possibility of outcompeting hybrid offspring.
