What you want to do is first run all the water into the pool through the softener, then empty out the water into the ground next to the well.
Do this quite a few times (20-30 to be safe), then wait a week or two. This will allow your demineralized water to filter through the ground back into the water table around your well, removing the salt.
At this stage, you then run the water straight into the pool, leaving you with softened water, but with no salt!
(Note: All of the above is said with tongue in cheek, and hopefully by this stage you should realize that is not what to do, but hey, maybe I should apply for a job at a pool store!! )
A water softener is not designed to handle thousands of gallons. If you are just topping off the pool you can use it, but otherwise it is going to be a challenge to keep it working through a fill (many recharge cycles).
Salt is not generally a problem unless your water is *very* hard, and then it is better than the alternative.
The best thing to do is to test the water with and without the softener and lookup the capacity of the softener between recharges. With that info in hand you can make a more informed decision.