I worked with DID patients for two years during my internship with Colin Ross, M.D. at Charter, Plano, TX.
You questioned if this person was actually DID. These people possess the "temperament" that enables them to perform. It was my opinion that some were faking in order to gain attention - it worked.
Those that do have DID are in need of long term therapy. Cognitive/Behavioral works the best as you are holding them accountable for their actions.
I would highly reccommend Dr. Ross' books. He has the most current thought in this area, and he is the leading authority. He runs the unit at Timberlawn, Dallas, Texas. My e-mail address is johnt3@flash.net.