Hi Brittany,
Did you ever find some more information on this?
From what I can find there is no way to 'load' a related table in the Flex App Builder UI, but it looks like this can be done via the API and I did find some samples. If that's the case though, I think I'll just stick with the js api as I thought Flex might be a way to do this a little quicker without much coding...
Warren M