Further... If the Space Nazi's got into Space before they were punished, and met some earth ships, isn't that a massive red flag that these assholes did something awful, a secret signal that was sent through time to all Earth ship Captains that these new aliens are not friends, they are ####s who need to be shot on sight.
Spinoff notes: I think the Cardassians, and obviously the Hirogen, were modeled on the Nazis. The answer seems to be that you can't prosecute a sovereign power for its past, unless you go to war and soundly defeat it first.