I'm afraid this could be kind of a pain. In Marketo, you could use a smart list to show the list of people who had gotten a certain email but that would not indicate the sender.
If you are synching these as activities to SFDC, you could do an SFDC report on activities and include the related Lead/Contact to see who received it. I believe the sender becomes the "assigned to" person of the activity so you could bucket it by sender this way (but test this to be sure).
The only challenge is that the SFDC activity will show the subject line of the email, (e.g., Was Sent Sales Email: Blahbedy Bloo) and so if you have different templates with similar subject lines it will be hard to distinguish them.