Is soft water from a home softener system ok to feed the pool auto leveler?

I would only connect the soft water to the auto-fill if you are having a problem with the pool water being 'too hard'. If you do not have hard water in the pool, there is no advantage in using soft-water for topup. You can use the soft water BUT you MUST maintain the correct level of calcium hardness in the pool water (200-275ppm is good). If the calcium hardness falls too low other problems can occur, including damage to plaster walls.