A lot of the contracts between the CMG and the hospital require the CMG to staff with only BC/BE physicians. Otherwise, you are correct, they would be greatly tempted to minimize their labor costs. It is theoretically possible for a FM/IM residency grad to work their way into one of these type-places (and I am not talking about those grandfathered into EM board certification.) It usually starts by working at a very rural affiliated hospital, getting a great reputation there, being invited to the "big city", and then developing a good enough reputation that you can be hired most places despite the residency/lack of board certification. BUT, today that is incredibly rare. It is like getting an EM residency with a Step 1 score of 195. You might be able to find one person who did that, so it is theoretically possible, but don't bank on it.