Good question. Is it?
I'm not a licensing expert, but I believe that the LCDS that comes with LiveCycle ES is only for use with the LiveCycle ES services. Its there for use when calling LiveCycle services as remoting end points and other ES functions, but not for other "non-ES" stuff.
In other words; If you want to build an AIR app that calls a process you built in LiveCycle ES using Flex remoting, then you are good. If you want to build a Flex app that uses LCDS to access a database via hibernate then you need to purchase a seperate license for LCDS.