Your question is an important one.

EMDR training per se does not include training in ego state therapy. Many EMDR therapists also get training in ego state therapy because it is a hand-in-glove fit, but it's not required.

Its important for anyone with complex DID to first and foremost work with someone trained in that condition, using ego state therapy or other methods as put forward by the issd (see www.issd.org). I like ego state therapy best.

EMDR should NOT be used early in the treatment of DID. The treatment of DID requires a phased approach with a careful emphasis on stabilization, containment, ego strengthening, resourcing, grounding and such, before trauma work is conducted with EMDR or any other method.

Once the DID client is stabilized and resourced, and the self-system is on board with the therapy and the trauma work, EMDR is often appropriate and profoundly life changing.

Finding the right therapist is easy in some areas than other areas. ISSD has a list of its members, but that doesn't require particular credentialing. Someone who is both a member of ISSD and EMDR trained Part I and II and advanced specialty training in the ego state methods with EMDR would be a good choice possibly.