Yes, members can have capture pages add contacts into a specific contact group. Also, they can transfer contacts betwen contact groups.
You are able to define a tracking campaign; the tracking information is included in the notification email that is sent and also stored in the members Area.
There is a section in the members area where you and your members can create url's to track different tracking campaigns when using a capture page.
Also, you can specify the tracking yourself by adding a hidden field to the form with the name "tracking" and for the value the title of the tracking campaign.
Also, you can append tracking details on the end of a URL of a page. For example if your URL looks like this:
To add a tracking campaign titled facebook you will add it to the end like this: