Hi Svenja,
honestly, I do not have experience on that, but what I know is:
- "redefine" creates a service based on a business object ("inside out"), the MPC and DPC being provided by GBI. Thus, I guess you are limited with respect to your entities and associations to what GBI expects to be relevant. It might be, that Cross-BO-associations are not in scope for GBI.
- SADL is based on an outside-in approach: You model your entities and their relations and lateron bind them to the BO model. This should give you much more flexibility. Technically, I don't see any reason why a Cross-BO-association should not be followed...
Cheers,
Oliver