The Satmar are a Hasidic group of Jews, bound together by a dynasty that was established in Hungary. It would be appropriate to call them fringe, but they're larger than the Neturei Karta sect of Judaism. I'd rather define them as extreme, not in the violent sense but in that they exist on the extreme end of a religiosity spectrum. They're very traditional and avoid contact the secular world as much as possible, without moving from New York or other metropolises they may inhabit. Unlike Chabad, another Hasidic group which gladly collaborates with secular Jews and even non-Jews, the Satmar are far more isolationist and skeptical of anyone outside their community (including other Jews).
Satmar is often brought up by outsiders who don't live anywhere near one because they're notably anti-Zionist. Or rather, anti-Zionist unless the Messiah delivers the Land of Israel to them, which they ultimately want. Their objection to Israel is mostly on theological grounds and their abhorrence to its secular aspects. However, unlike other anti-Zionist groups of Jews, they don't make as huge a stink over it. They don't go out of their way to be anti-Israel and don't jump at the opportunity to attend rallies against it. They're passive and just boycott the State, rather than Neturai Karta which takes a much more active approach.
As for not being on national TV: They HATE secular culture and TV is something they've always avoided. If you wanted to put them on TV, you'd have to do a lot of convincing as to what you're talking to them about. And, as another non-representative sect of nationwide or even worldwide Jewry, no one would really want to talk to them especially given their aversion and isolationism. They don't even represent Jewish anti-Zionism all that well, so a contributor who is specifically Satmar wouldn't really be sought out.