I can't say definitively that they serve their intended purpose, but they're intended to replicate the added complexity you get from fermenting with bugs.
I assume that's why they are added as well but it doesn't really make sense to add crystal malt to a beer that is trying to replicate a beer style that is very dry. I guess I can understand the smoked malt or some dark malts that add tannins that create sort of a dry feel. I guess if you're trying to recreate Lindeman's fruit stuff it has a thicker feel from all the backsweetening...
Well, here is my first all grain Framboise Lambic. I used 9lbs of fresh raspberry too. This Lambic reminds me of Lindeman's Framboise Lambic. Thanks Biocemetic for the link with the recipe and thanks to all for your suggestions.