why not? if it's low in fat and sugar, has live active cultures and no high fructose corn syrup - then heck yeah! there's lots of good natural brands on the market.
It would really depend on the ingredients. Some frozen yogurts are high in sugar. The best is always to make your own, using plain yogurt, blended fruit, and the sweetener that you choose (like agave or stevia).
And they do still have carbs (very simple) and calories. I only have them when I have a yogurt craving. If you are fighting sugars you may be low on essential fatty acids such as fish oil or evening primrose oil or flaxseed oil. They do have some calories but they are good for you.