A private clinician certainly can give an IMO and complete the DBQ for PTSD.
PTSD is a subset of anxiety DOs, which is a subset of mood DO's.
In addition, my decision states, and i quote: "Greater weight is assigned the treatment records of Dr. X as opposed to the benefits questionnaires as they were completed in a clinical setting and contained more detailed rationale."
Dr. X being the redacted name of the clinician whom I paid to complete both my IMO and fill the DBQs, to be clear.
I filled out literally hundreds of exam requests, including PTSD, as a VSR and *most* of them went to private contractors (VES, etc), not the VA facility, so if this were a rule, which it's not, the VA, itself, is breaking it every minute of every day.
Come up with a CFR, manual reference. I'm not sure why this false assertion continues to get spread on this site.