My team has been researching the ability for Eloqua to add logic to only pass fields from Eloqua to Salesforce if they are not blank or the target SFDC field is not blank.  Unfortunately, we concluded it is not possible from the Eloqua end to do this. This could significantly impact the contact record if we send lead activity data back for a known SFDC contact, as we don’t write the existing SFDC data to our contact record since we can’t do prioritized overwrite rules in Eloqua.
 
Does anyone know if there is a way for Salesforce to manage this for the incoming data source? Is it possible to set logic on designated lead and contact fields to only accept Eloqua data if it is not blank, and for specific fields only if SFDC is blank?