You can assess what leads were created via social form fill out by pulling a smart list using a "lead was created" filter, adding a constraint, source type = Social App. However, there are some known bugs regarding the social form fill out that you should be aware of.
If a lead elects to fill out the form using the social option, but abandons the form and doesn't click submit, they will still be added to the database. Unfortunately, there is no record of the lead filling out the form and lead source, axquisition program, etc. are not written to as they would be had the lead submitted the form. If you are dealing with international leads, this can be hazardous as it is a violation of CAN-SPAM laws.
Hope this helps!
Tara