Program attribution

Not necessarily. Because programs can be used for many activities, including inbound and outbound campaigns, as well as data management activities, program membership does not occur by default. In other words, depending on the program, different criteria may constitute a "member", and those aren't always related to an email. You must use the flow action in a smart campaign "Change progression status" to actually add a name as a member of a program.

So for your email program to assign a recipient as a member of the program, you should follow the "Send email" action of your smart campaign with a "change status in progression" flowstep that adds them with a status of "sent".
Hope this helps!

-Jeff

Jeff is correct above.  But I also would like to add that if you create a campaign in SFDC with members, and sync it to a program in Marketo, they become members of the program. 

Yes, glad you made that distinction Michelle, I had forgotten to mention it :).

Thank you for the input. 

There may be others I've missed, but these are the primary ways I'm aware of for a person to become a member of a Program...

1. Change Progression Status flow step
2. Importing a list directly to a program and setting the progression status
3. Filling out a form that's a local asset of a given program