Yes, a Seyid male/female is allowed to marry a non-Seyid male/female. There is nowhere in our religion that somehow forces Seyids/Seyidahs to marry someone like them. This has also unfortunately turned into a very negative culture as well. The esteemed Marja' A.U. Seyid Sistani has pointed to this in a statement where he admonished some parents who cling onto this wrong culture and reject prospect spouses on the basis that they are not Seyids/Seyidahs.
With prayers for your success.