No. You will record something but it will just be a chunk of serialised data and would not be realistic to play back.
If you can develop using the flex libraries a way to parse this data correctly you have a solution. You have to look at commercial software for flex support.
I have used OpenSTA for flex applications with no problems. It works as Steve suggested. Perhaps Adam has run into some specific problem that I did not encounter. If so Adam, please post an example of OpenSTA failing to work with a flex app.
If you're using Flex with a straight XML based protocol, then it'll be no problem. But if you're running Flex over a protocol such as HTTPInvocation, which is a serialized format, then it will record but will provide encoded responses. This makes it near impossible to parameterize your scripts. Maybe this is what's happening to Adam?