Marketo <> Mulesoft <> Dynamics Integration

Hello Community!

Curious to see if anyone has ever had experience implementing middleware (in this case Mulesoft) to Marketo and back to Dynamics On-prem? 

Doesn't the Marketo Sync User have to be created in the Marketo instance as well (similar to that of a standard Salesforce integration)? Or can the Marketo Sync User be created only in Dynamics. In this case, client is using a custom sync filter created in Dynamics on customer and lead entities named “new_synctomkto” that is used to control the leads/customers that sync from Dynamics to Marketo. My fear with this is that sync will NOT be bi-directional. There are no lead create triggers yet in Marketo.

Thanks!

Kristina