Even ignoring the racism, since when does “not ever having done something before” constitute a “tradition”? I’ve never eaten yogurt but that doesn’t make it a freaking tradition.
So I guess there's a kind of deniability here in that those people aren't going to identify themselves and, if they are identified, they can always say that race wasn't the reason, that it was just that they weren't "our kind of people," that this wasn't the sort of wedding you wanted to have here, or something of that sort.