Water from the hose should be fine. You can tell if it's hooked up to the softener or not by tracing the pipe the hose tap connects to. If the pipe to the hose comes from the piping after the water softener, it's soft water.
If it's connected to the water pipe BEFORE the water softener it will be, I assume, hard well water. I'd guess it's pretty hard or you would not have the water softener. Snails will like it fine.
I'm amazed any fish are doing ok in water from a softener. I am no expert in how the machines do what they do, but calcium is one of the two main minerals that makes water hard. If you have a softener, you put big bags of salt into it every so often. The water coming from the well goes through the machine, which mixes the water and salt in some way, so that when it comes out, all the calcium is gone, replaced with part of the salt. Salt is not one thing, it's sodium chloride.. the sodium is what goes into the tap water, I think. So you need less detergent to do the wash, soap lathers easily, your skin feels nicer after you bathe or shower.
But regardless of how the water softener works, it removes calcium. Any fish or critter than needs hard water and calcium is not going to do very well in soft water from a softener. The Betta may be ok simply because it's not a fish that must have hard water, but snails do need hard water, or they can't maintain their shells. Shrimp would have the same problem and wouldn't be able to moult.
Not knowing what fish your Dad keeps, I can't comment, but most manufacturers of water softeners will tell you not to use the water for fish, and most of them tell you not to hook up the garden tap to the softener, because you will be paying so much more to soften water used for the garden and yard, where it makes no difference how hard it is.
