I've found the site to have some questionable sources (Not limited to the book "White Women, Black Men: Illicit Sex In The Nineteenth-Century South" which is already a dubious title in of itself). Exactly how accurate is the site as a whole in regards to the lives of enslaved african-americans in the Antebellum South, particularly Maryland & Delaware?
Are there any specific claims you are asking about? There is a lot of content to sift through there, which seems to mostly be digitized primary sources such as census records. But at the very least I can say White Women, Black Men: Illicit Sex In The Nineteenth-Century South is a respected academic work that was well reviewed upon its publication in the late '90s, although I'm not sure what makes the title seem so dubious in any case. See a sampling of reviews such as:
Silber, Nina. “White Women, Black Men: Illicit Sex in the Nineteenth-Century South.(Review).” Journal of American History. Organization of American Historians, September 1, 1999.
or
“Martha Hodes. White Women, Black Men: Illicit Sex in the Nineteenth-Century South. New Haven: Yale University Press. 1997. Pp. Xii, 338.” The American Historical Review, February 1, 1999.