Hey Hank, I'm almost certain that Marketo will only recognize the native Lead Owner field for integrations with SFDC and Dynamics CRM. That said, you can create a new field for lead owner and assign based on your logic above. You just won't be able to use the fields that already exist in Marketo.
Change Data Value: Option
A. If member of list/smartlist [your list], then change Lead Owner (new field you created) to Agent A
Otherwise, change Lead Owner (same new field created above) to Agent B
Thanks Dory. With SugarCRM integration, I can set one of our field values (SugarCRM Owner Email) which in turn will assign the lead in Sugar. Since I posted this, support reminded me how I can set that field value based on the logic I needed.