No. You don't need FDS.
Let me ask you another question: how do you currently connect
to your Access DB in your WEB APP? JEE, .NET, ColdFusion, PHP...?
You'd keep your server side code as it is, let's just say in
.NET. And hit the application url using Flex frameworks HTTPService
class. This is exactly like using Ajax to get data from server
side.
ATTA