No one is considering arresting Obama. In fact it is likely impossible and most probably inadvisable. In fact it would be ludicrous to think of arresting Obama because of the separation of powers doctrine.
What US Marshals can do is to serve arrest warrants or summons on federal contractors that are involved in making the amnesty ID Cards which lead to SSNs. Federal contractors are fair game and cannot escape jurisdiction of a federal court order.
The cards are already illegal per the Simpson/Mazzoli act.