This is very interesting indeed. I am from Alabama, but my Moultries are from South Carolina. I can place them in South Carolina as early as 1802. Even in Alabama, the Moultries and the Singletons are together in the same township and living and marrying across the surnames. From the website you posted, I see that they were together in South Carolina as well.
I have read "Slaves in the Family" by Edward Ball and there are so many similarities but I have not been able to trace slave records of my Moultries to their owners in South Carolina. Very interesting reading though.