These are the standard of care treatment guidelines for DID:
https://www.isst-d.org/wp-content/uploa ... ED2011.pdfAs long as the treatment follows those principles (all alters are equally important, etc), it can draw from different approaches like IFS. As Nondescript said, IFS can be adapted to work for DID, even though it was developed to help with ego states of singletons.
When IFS is used for people without DID, I think the concept of the core self is taken more literally, as being the "main" personality, with the (non-dissociated) parts being sub-personalities. Obviously, that wouldn't work with DID, where all the parts are alters, including the host, and all are equally important clients of the therapist.