I think this would be a bit difficult in modern Australia, which WAS my whole point. Disgusting as the Croatian celebration is, the likelihood of any harm's resulting to Serbian-Australians seems very limited.
"Physical harm" in the light of day, probably not.
But hate-groups make members bolder about their bigotry and make their target victims either scared, angry or both (fight or flight). I think that it does increase the likelihood of a confrontation of some kind by somebody.
If you are a Jew and see people openly celebrating Hitler, or you are Black and see the Klu Klux Klan partying in the open and celebrating their evil deeds, it does have an affect on you whether you want it to or not.