It depends. HappyGirl's right that there can be a lot of calories in fruit because of the natural sugars. However, if you're having fruit in lieu of a bowl of pasta or a couple of sandwiches it might still end up being a lower calorie alternative.
As to whether the fruit will damage your weight loss, it really depends on what 'system' you're using to lose weight. Back when I was on Weight Watchers NoCount I could eat all the fruit and veg I wanted between meals, I lost weight doing it, but granted I wasn't eating as much fruit as you are. Other, more traditional, weight loss methods recommend all the vegetables you want but no more than two pieces of fruit per day (vegetables are a lot lower in calories than fruit because they don't contain as much fructose). Low carb diets cut it down even more than that. As to which way is best, I'd simply recommend chosing one that a) helps you lose weight and b) you can happily stick to long term.
Personally I think a huge bowl of fruit salad and yoghurt sounds like a very healthy lunch. There is fibre and carbs in the fruit and protein in the yoghurt. In my opinion you just need to be careful not to overeat, though. If you eat until you're bursting you might want to try a smaller bowl!
In the end there's only one way to tell if it's sabotaging your weight loss and that's to 'suck it and see'! If you still lose weight at a healthy pace while eating a huge bowl of fruit salad and yoghurt every lunch then I don't see any reason to change. If you plateau or start gaining weight it might be worth trying something else for a week or two to see if that's the problem.