It is my understanding that Diabetes Centers are accredited and that these centers have a "lock" on insurance reimbursement, namely many insurance companies will only cover education from an accredited program. I believe these programs must teach the MNT provided by the ADA/ADtA. My local center's director has told me this is the reason that they adhere to the guidance.
But as PatientX notes, you can go to a dietician and they are free to speak the truth. All they have to do is echo back whatever mantra is required for individual certification. I'd be interested in how many have had success getting insurance coverage for individual RDs or CDEs who are not part of an accredited program.
ps. PatientX, you look like a regular. Did you change your name?