It is true that many of the doctors used by SSA, for these evaluations, are not as competent or as thorough as one would hope. Therefore it is quite important that, under SSA regulations, you have the choice of having your own treating phsycian or specialist (MD, DO, or clinical psychology only).

As long as your doc is available, qualified and willing to perform said exam (for the small sum that DDS usually pays), you can insist that your doc be allowed to do it.

Unless your treating doc is unsupportive of your disability claim, you are almost always better off performing any requested examination that SSA or DDSs deems necessary.