So yeah, Buzzfeed says "I am not going to contact the Danish Frisbee Sports Union to ask them if this is a real ad, but you're welcome to." . But we don't have to, because we remember when this was entered in the The Danish Young Creative Circle Awards 2011 - and we have it posted here back in 2011.
In 2012 they sent it to the Chip Chop awards, and now it's viral. For more (real) ads with Hitler in them use the search function, we have plenty.