I’m not sure yet whether the Flash API works directly with Flex, since it’s written in ActionScript 2. However, in looking through the API, I think you may not need the Flash toolkit at all within Flex, since the “standard” API is accessed through HTTP and XML, which is built into Flex.
Does anyone know more about the Digg Flash API? Do you need it for Flex? I happen to know one of the founders of Stamen from my DJ days, so I’ll be asking him as well.