If you are receiving, or about to receive, SSDI at the time you settle, the CMS will require a review to determine the amount of a set-aside--money to be taken from the settlement and put in trust to cover future medical expenses. This is only if you are settling you indemnity and medical. If you settle only the indemnity payments, there is no need for a CMS review, as the medical continues. Some carrier are willing to do that type of settlement. If there is a CMS set-aside, that amount must be expended on causally-related medical expenses before Medicare will pick up.
If you start receiving SSDI payments, and wish to pursue rehab, SSDI has a plan whereby you can attempt a return to work and not jeopardize your payments. If the job is not possible with your disability, you would return to SSDI payments without penalty. It's the ticket-to-work program. If you go to the SSD site, you'll find plenty of information.
You're confused, and so is the rest of the world. This is a complicated mess we've created. There are many curves that can be thrown. When you say you are only getting bits and pieces of information from your attorney, that sounds about right. No one has a complete handle on this, and rules are changed frequently. When you add into the mix the fact that each worker's situation is unique, from their past work experience to their current medical condition, it just makes it that much more difficult to evaluate a situation and advise how the myriad folks involved (carrier, Special Fund, CMS, WCB, SSD, etc) will treat any particular situation.
Good luck . . .