Is it possible to Email CC from a Contact Lookup field on a Contact in SFDC?

Well, Marketo only allows using the Email type fields in the Email > Email CC Settings. I don't think you'd be able to choose the string/text/lookup field synced over to Marketo from SFDC in the Email CC settings. You'd need to create it as the Email type and map it with a custom email type field in Marketo or use it as an unmapped SFDC custom field in Marketo. Alternatively, you'd need to create campaigns to write data from the synced non-email SFDC field to a custom email field in Marketo (of course, you'd need to ensure that the data in the SFDC field is a valid email address). Check out this article on Marketo Email CC FYR.