Your atty can contest that request and indicate the facts as you described them. why aren't you asking your atty who knows your case?
The information you obtain from this website is not legal advice.
A finding by the SSA that one is disabled IS often considered top evidence by a family law judge, given the difficulty of proving complete disability before the SSA. However, there is no law, generally, that requires the judge to accept it. If I were you, I'd consider getting a letter from your treating physician(s) who know your condition better than any "evaluating" doctor, to explain how your condition remains as it was back in 2008. Your ex may not be totally out of line, given that the SSA has not reviewed your case since 2008, and certainly people often improve over time to be able to go back to work. If you HAVE undergone a CDR with the SSA, and you prevailed, I'd bring that paperwork to the Judge's attention, to show that you have been reviewed (your condition) and found to still be disabled.
On the SS front: You may also want to retain a firm that provides ongoing benefits protection services to enable to you have the strongest case possible when you are confronted with your next CDR with the SSA.
I think your ex's attorney is completely out of line here. There is no legal precedent that will require you to do this. For example, who will select the so called IME doctor? What is the extent of the proposed IME? What disability standards will be used to define if you are able or unable to work?
Perhaps you don't have a lawyer? If so, get one so you are not subjected to these types of shenanigans.