Having played RO since early 2007, I've only seen a few neo-Nazis in the realism community. Preaching their beliefs is generally regarded as unacceptable within the Axis realism community, but, as always, there are rare exceptions to the rule.
I have, however, seen a significant degree of neo-Nazi pubbers and some clanners as well. Often times, the pubbers are quite a bit more vocal about it - likely due to their relative anonymity as a pubber. They're in the community at large, certainly not isolated to realism units.
There is undeniably a large stigma attached to German realism units, though. As a former member of the 2.SS, I had pubbers and clanners outright accuse me of being a Nazi, insult me... Few ever listened when I explained that we weren't politically or ideologically motivated. I'm sure someone's probably going to say, "Well, you should expect that if you were in an SS unit.", but the presumptuous attitude of the community towards anyone with a German tag is rather frustrating at times.
And then there's the attitude towards realism play as a whole, which we've been addressing here in this topic. When Hertz and I first started our unit, we encountered immediate derision and snobbishness on servers we played on. I don't believe it can be explained by the sudden influx of new players into the game, because I've seen veteran players of Red Orchestra with the same viewpoint.
Simply put, it makes little sense to me that anyone can really take a superior attitude towards the realism community, when the game itself fosters a more authentic, realistic style of gameplay. It's more logical for realism units to develop from this game than from, say, Call of Duty or Counterstrike, which also have their own realism communities. Yet, a good number of the Red Orchestra community act as if we take the game too seriously if we try for a historical infantry set-up and use tactics now and then.