When creating an IEPD are the processes different between NIEM and GJXDM?

Conceptually, the IEPD lifecycle in NIEM (as defined in the NIEM Concept of Operations) is very similar to the IEPD lifecycle followed by many IEPD developers in GJXDM.  The GJXDM lifecycle is documented in the GJXDM Users Guide.
Both lifecycles call for the basic steps of understanding the contextual business scenarios or context of exchange, documenting exchange requirements, modeling the information being exchanged, mapping the information model to GJXDM or NIEM, and building schemas from the mapping.  Both lifecycles suggest (the NIEM lifecycle does so explicitly) that IEPDs should be published and registered so that others may find and reuse them.
The NIEM lifecycle references supporting tools that were not available in the GJXDM lifecycle, such as the NIEM Naming and Design Rules (NDR) and the NIEM Component Mapping Template (CMT).
The GJXDM lifecycle makes more explicit reference to the benefit of logical domain modeling as a way of capturing information requirements that are independent of the XML vocabulary.  The domain model represents the requirements that are mapped to GJXDM (or NIEM).