No, I don't think its racist, and if might be a very interesting game if it played the adventure angle straight. But the 'historically accurate' slave tetris is just a terrible idea.
Awful.
All I could think to trump that would be tetris-ing corpses into a mass grave for bonus points.

Killer Joe: The Monty Python and the Holy Grail game does exactly what you said in the last paragraph. The long pieces sometimes move on their own a bit and say, "I'm not dead!" None of that was a joke.

Unfortunately, it WAS pretty historically accurate. That's really the horrible part of it.

http://images.fineartamerica.com/images-medium-large/slavery-s lave-ships-granger.jpg

Thats incredible. I bet you the guys who drew up that plan even thought they were being very generous and humanitarian as each slave has enough room to lie down. They could pack in even more if they all had to stand.

Nah, I bet he just realized more of them would die on the way if they stood, I doubt it had anything to do with anything other than profit margins.

Basically, think "what would Wal-Mart do with their workers if they were completely unburdened by legal regulations?" and you'll get in the same ballpark.