The thing about snails is they're one of the primary carriers of certain parasites that infect fish. Shellcrackers love them; the part of Santee-Cooper lake in SC that produced the world-record shellcracker had had a recent influx of Zebra mussels shortly before the record. They could possibly be okay if you had a good number of shellcracker in the pond; oftentimes they'll find their way to a pond without help, much in the way frogs do.
Salamanders, on the other hand, I think are a great idea. I've pondered more than once myself stocking them as additional bass forage; it's been proven bass love them, and I'm not aware of any drawbacks they pose (though that doesn't mean there aren't any).
TS I'm sure would be fine in your pond. Bass definitely love them.
