I think the only way you can compare the two is by saying that both are singling out one group of people. However, the Jim Crow Laws just seem to sort of just say what the blacks couldn't do. The only slight similarity I see is between the interracial marriages where the Jim Crow laws say that if you've married someone who is just 1/8 black, then the marriage doesn't count. But then I remember, those very precise Nuremberg Laws which weren't at all confusing, it was indicated that if you were indeed already married to a Jew, you may be considered Jewish also. And then, if you were married to a Jew, you would have to do "hard labor" (i.e. concentration camps). But basically, the two both forbid the blacks and Jews from mixing in with the whites and Germans. In the case of the Jews, the laws were a lot, lot more harsh and tried to be more accurate, but they came out really confusing in some aspects. In both though something I've noticed, is that the people making these laws, trying to keep the peoples apart are treating the targeted group as if they are not really people, and they have no say in how they are treated, that they should just go along with this harsh treatment. Though the Jim Crow laws are wrong, they do not really compare so much to the Nuremberg Laws. On the whole, all the Jim Crow laws are saying is to seperate different institutions amongst the whites and blacks so they never have to deal with one another. This is not fair by any mean, but when you think about it, there was so much prejudice in the south against blacks, that if some of these laws didn't exist, then there might have been even more gang attacks on blacks.However, there are other laws there saying a black can't be buried amongst whites. Now such things as this law are ridiculous. That is definitely pushing it, and that is basically what the Jim Crow Laws seem to do, just keep trying to push the blacks to the edge, and see how far they can actually go.
Then, the Nuremberg Laws basically come out saying all the ways you can be determined a Jew, few of which are actually clear, and the penalties which come as a result. And then they set restrictions upon the Jews. They are extremely harsh and unjust, and completely unacceptable. They take penalties a lot further and are more unfair.So to conclude, you can compare the two based on the fact that they both set restrictions for certain groups and discriminate against them very clearly, but you cannot compare them based on degree of penalties/strictness. The Nuremberg Laws far exceeds the Jim Crow Laws on the basis of injustice and the scale to which one is penalized for not following the laws. And yes, something akin to the Holocaust could most definitely have happened in the United States.