If you want to pass it so something off of IS, like you need to look at how it will be serialized on the way and that is dependent on the transport that will be used. Developer to IS communication used the IDataBinCoder.
If the object is in the pipeline when returning to Developer (either when stepping through a Flow or in the final output of a service), classes that support one of the many interfaces that IDataBinCoder supports will be serialized. The final option is to try Java Serialization, which would require the object to be on Developer in order to do a Java readObject on the client-side.
When running a service, the object will still be an object while in the pipeline, so it can be passed to another service fine.