I am reading Thomas Sowell's book, Black Rednecks and White Liberals. While I dont know yet if this situation is mentioned with Jefferson it can be surmised some 50 pages in that former slaves of men like Jefferson led much better lives then other Southern blacks and the Hemmings case would prove it true also.
I am reading McCullough's book on John Adams. When Jefferson returned to Monticello after a long stay in France, his slaves picked him up joyfully and carried him into the house. On the other hand, Jefferson was overly enthusiastic about France back then.