You would need to check the specific marriage requirements in South Carolina. However, in general most states do not prohibit undocumented aliens from marrying. As to whether your fiancee could seek immigration status after you marry more information is needed including his manner of entry, immigration history, criminal history, etc. President Obama has passed no new laws; the President only has the power to sign into law legislation passed by Congress. President Obama has created a program that allows certain qualifying individuals to remain in the United States and obtain employment authorization, but this program confers no legal status. I would encourage you and your fiancee to schedule a consultation with an experienced immigration attorney.