Good day Greg!
Apologies - when I was replying last night I had misread your initial question to mean that you couldn't merge in DCRM. Next time I go to reply I will wait until I get a good night's sleep and re-read first!
I had a client a few years ago that had an issue merging records in DCRM because of a custom plugin they had deployed. Their only course of action was to delete the DCRM record, and we then had a smart campaign in Marketo to run clean up for records marked as Microsoft is Deleted.
Merging in DCRM is the best approach as noted by you and Dan Stevens. I don't know of any CRM Fusion Demand Tools like applications for DCRM, perhaps we should build one!
Hoping to see you at Summit next month!
I'm not sure if you have find out a solution yet which will DeDupe your records with Marketo and MS-Dynamics.
Our product M-Clean which earlier was providing DeDupe facility for Marketo and Salesforce, is now capable of doing this with Marketo and MS-Dynamics.
You can follow the link above and can see other features of the product, can request a demo and if found reasonable and solving the needs, then can opt for it.
Grégoire Michel - we had a demo and did some testing with M-Clean several months ago and it didn't work for MSD records in Marketo. We're about to test this once again - using a variety of duplicate scenarios (Marketo person/CRM contact, duplicate contacts, duplicate leads, duplicate lead AND contact (note, merging multiple entities - like a lead with a contact - can't even be done natively on the MSD side - so it will be interesting how they accomplish this from within Marketo). Once we have our next demo, I'll report my findings back to the community.