Certain styles require soft water (Pils), but in that case it means water with almost no minerals, not "softened" water. Most water softeners use salt, which probably wouldn't be a problem. I would taste the water ahead of the softener & if it doesn't have any off flavors use that. Yeast does need some minerals to grow.
Neither Miller or Palmer spends much time discussing water other than saying the water shouldn't taste bad and the pH should be around 5.2. If it tastes bad , run it through an activated charcoal filter.
I've read long articles about water. About all they say is summerized above.