Just to add to my previous post, these were the findings of immigrant slave owners in Rapides Parish, Lousisiana, according to the 1860 census:

Slave Owner Place of Birth//Number From this country

Africa 1
Belgium 4
Canada 1
England 3
France 7
Germany 5
Ireland 21
Scotland 3
Trinidad 1

Rapides Parish was one of the largest slave holding parishes in the entire state of Louisiana. Louisiana also had a substantial influx of German immigrants, to the point that one of the parishes was at one point known as the "German Coast."
It is my opinion, based on my research and on what I have read, that German involvement in slavery in the U.S. was minimal when compared to other European ethnic groups.