What percentage would you estimate experienced anti-semitism from people affiliated with or even sympathizers of the groups listed by SPLC vs. groups that they don't even have a category for? Personally, I have experienced anti-semitism a number of times and only one do I even consider it a possibility, albeit with no indication one way or another, that they would at all sympathize with a neo-nazi group.
It depends on where you are.
I think it's clear from the responses there and my anecdotal knowledge, in the US a visible Jew is most likely to experience antisemitism from black or Hispanic people, with a tiny fraction experiencing it from right wing neo Nazi types.
In other countries, you're more likely to experience it from Islamic people, and in others, neo Nazis.