Yeah, the problem with adding fruit is that you don't get net much, if any, additional alcohol because you are also adding water with the sugar.
Whole fruit is roughly 10ppg. If you are adding more than one pound per gallon wort, you aren't significantly affecting the ABV of a beer. Fruit purée has a greater ppg, but it's still not enough to raise the ABV much.
And when you run the calculation, it doesn't matter if you assume you add it before or after primary fermentation is complete. It works out to the same value either way.