As far as I know, all varieties of incarnata produce edible fruit. But since the species is wild, there's a wide variation as to the quality of the fruit (just as the flowers show a wide variety). So if you got p. incarnata var. alba (which isn't a subspecies, just a variety) the fruit may be great, may be mediocre, but it'd be edible.

I recall reading somewhere that 'Alba' is said to produce very good tasting fruit.

Does anyone on these boards have an Alba to trade? I've got some rooted cuttings of Lady Margaret I'd be willing to swap for one.