When data is synced to Marketo from lookup fields in Dynamics, the unique record GUID is put in the Marketo field rather than the name of the referenced record.
In Dynamics, the data stored in lookup fields is actually the unique ID of the referenced record. Since the record that is being referenced is also in Dynamics, the UI is able to display the name of the record rather than its unique ID. However, when the data for those fields is pushed to Marketo, it is still the unique IDs that are synced over, so you will see the long string of letters and numbers in the associated Marketo fields, and not the name of the records. A workaround for this behavior is to:
Create custom fields in your CRM for each of the lookup fields that you intend to sync.
Create a workflow in Dynamics that populates those fields with the name of the referenced record, and stores it as a string of text. When those fields custom fields are synced to Marketo, the data will be displayed as the text that you want instead of the unique IDs.