Well the reason it shouldn't be done with grapes was said to be because it could water them down lowering the Sugar and acid levels.
But if your making fruit wine, isn't the majority of it from concentrate anyway? .....
Not at all. My fruit wine is made from whole fruits. With my peach wine the only water I use is to dissolve the sugar for a simple syrup which amounts to 1 cup per gallon approximately. I use a concentrate for Black Current, and Cherry wines only because I don't have access those as fresh fruit at a reasonable price. All others are made from the fresh fruit only with only the minimum amount of water needed.
Secondly if I wash fruit I drain off the excess water - Lay the fruit on a towell until I'm ready to press or cut it up. So there is at most maybe 1/4 cup of water if I have a lot of fruit. When I pressed apples, again I only added the water in the simple syrup (6-7 cups of cut apples has given me right at 1 quart of apple juice. I don't put the fruit and water into my bucket. Washing fruit doesn't have to dilute anything if the water is allowed to drain off.
For fruits like blueberries, blackberries, black raspberries I never wash the fruit because it comes from our own bushes and vines, I know what if any chemicals have been anywhere near the plants. BUT with those last 3 fruits, they need water added because using 7-9 lbs of fruit per gallon of those plants
is really wasteful in my opinion, 5-6 lbs of black berries, 5-6 lbs of blueberries or 5-6 lbs of black raspberries is plenty for a solid full bodied wine. In fact the most difficult batch of wine to keep balanced was a batch of blueberry made with 8 lbs per gallon, the acidity was crazy low from the start.
So the answer = No one way works for every situation.