Solution Documentation Service Task <-> Executable Library

We have a requirement to model a process step that has a task type of "service" that will validate a clients account balance. The service is provisioned by a function module that was developed by our application team in ECC. Since classes or functions are not defined as a Library Element Types in the executable library would you assign the development object directly to the process step with no associated executable?

If I extended this as a rule could I say that the executable library is meant more for user tasks?

Thanks, Andrew