I think traditionally, none. You might find some usage somewhere nowadays, but not often.Which German beers would traditionally be made using caramel malts, then? From what I've gathered from forums and online resources, caramel malts are not used for Münchner Dunkel or Altbier or Schwarzbier or Bockbier. I haven't read too much concerning (Dunkles) Weißbier, but it doesn't seem more plausible than for Münchner Dunkel, I'd say.
Exports are certainly a factor. But Belgium and England seem to have a rather rich tradition of producing their own malts. Besides, I'm somewhat sceptical if post-WWII Belgian brewers would buy German malts; with everything that had happened. Maybe the Czech republic?
Also, because it just popped into my head when I saw the thread's title and I always enjoy annoying people: "What is Alt? Oh baby, don't hurt me!"