I have used fresh fruit in the past with good success. Typically the goal is to add a particular flavour to the beer. Adding fruit should not impact beer sweetness, as the sugar in fruit is fermentable, and you need to add non-fermentable sugar to increase sweetness.
To add fruit, heat fruit in a little water to 160 fahrenheit and allow to cool in a closed container. Add to fermenter once cool. Heating to 160 should kill all the microbes, and not affect flavour too much.