The computer software is not an issue. Most of the service software can read the codes, and show what is wrong. The dealers software can write to the ECM and the body computer.
As for the independent dealers, I would still call the two Mercedes dealers, talk to their service managers and ask them if they can recommend a mechanic - they may be able to help you out. All Mercedes dealers have access to repair info and parts for all Mercedes vehicles and a few can even order Dodge parts that the dealer says are not longer for sale. I know that I can order parts for vehicles even coming under the gray market laws here but the dealers refuse to service them because they lost a sale - parts are a little different. You last bet would be calling Mercedes and seeing if they know of a mechanic. I used to be registered with them and got a few new customers through their system.
You know I really wish that Mercedes would bring their entire truck line here to the states.
Makes me want to go back to Mercedes training with all this money being thrown around.
As for Dodge and the Alpha dealer, come on OVM, up here they still haven't figured out what customer service is and how to not argue with the customer or charge them for things they didn't do. I gave up on American car dealerships a long time ago.