Sales Owner Fields?

Just an FYI here, I've seen variations of this.  Perhaps it's a subscription thing?

What I can tell you though is that if you're looking at field management to see what the mappings are, you won't see anything here.  These are system managed fields and the mapping is performed and managed by the system.

The best way for you find the answer to your question is to test it out.  Change owners on your CRM and see what syncs down.  Use the Change Owner flow action in Marketo and see if it works and see what syncs up to your CRM.

Jim is correct, "Sales Owner" is the name of the lead/contact owner fields reserved for CRM integrations. In newer instances "Sales Owner" fields have replaced "Lead Owner" fields."Account Owner" is the same. 

If you've synced to Salesforce or Dynamics, you can used the "Sales Owner" fields as tokens to personalize an email  from a rep or to send alerts to the lead or contact owner.

If you have a custom integration, you are able to use the API to populated those fields.

If you aren't synced to a CRM and are standalone, then you won't be able to use those fields since they're "reserved" for integrations. In that case you'll want to create your own custom fields to personalize by lead/contact/sales owner and if you're sending alerts you'll use the "None" option and send to an email address you enter in the other emails field.

Are you sure these sfdc records are owned by a sfdc USER?

If the record belongs to a QUEUE, the 'Sales Owner' name and email fields will be blank in Marketo.

This makes sense as you wouldn't want to personalize an email as coming from or referencing "US Marketing Qualified Queue", etc. in an email.