|> I really can't see why this name isn't disallowed... In Poland, he could even go to jail for openly identifying with Hitler.
Not really. First, Warlight servers are not (probably) located in Poland, and Polish right doesn't really have much to do here. Second, It'd have to be open "promotion" of nazism or similar system (it doesn't have anything to do with Hitler himself), and I highly doubt any court would sentence anyone to jail time for using "Hitler" for a nickname and his photo for an avatar.
Let me cite an excerpt from the Penal Code (Kodeks Karny - I'm not certain of that translation):
|> Kto publicznie propaguje faszystowski lub inny totalitarny ustrój państwa lub nawołuje do nienawiści na tle różnic narodowościowych, etnicznych, rasowych, wyznaniowych albo ze względu na bezwyznaniowość, podlega grzywnie, karze ograniczenia wolności albo pozbawienia wolności do lat 2.
My rough translation for English-speakers here:
|> Who publicly promotes fascist or other totalitarian political system or incites hatred on national, ethnic, racial or religious grounds can be subjected to a fine, restriction of freedom or imprisonment up to 2 years.
There's also an article in the Constitution which explicitly disallows existence of political parties and other organizations referencing fascism, nazism and communism (and some other things in similar vein which are not important here).
(I'm a Pole too, if you haven't guessed by now ;) )