I don't necessarily think it would be a paradox, as normally the whole idea behind time travel is that the travel itself is 'outside' or 'seperate' from the real-history events. So if you killed Hitler, only you/the people traveling within the 'seperate' universe would notice, and major events would occur/ceace to occur.
(That being said, I probably wouldn't kill Hitler anyway as many human rights' laws have come because of him, if he never existed then an event like that could happen in a much more modern world where technology makes it a million times worse).