Preface: Every (or almost every) ideology of every sort has some followers who take it to the violent end. The difference between a "dangerous" Ideology and a peaceful ideology would therefore be in the amount or percentage of violent followers that it creates rather than "if" any of its followers are violent.
Some violence exists in the fringes of the fringes of some Jewish religious groups, with most of it being "moderate" violence - not including intentional harm to people's lives but rather protesters blocking traffic, etc.
Disclaimer: Since I happen to know more than Wikipedia on the following content, I can only quote myself (maybe copy this answer to Wiki and provide this answer as a source, I just know too much more than NYT reporters on this subject, can't help if you don't believe me).
Introduction to Orthodox Jewish groups (in an attempt to help people who seem to know very little, I'm explaining more than necessary to answer the question): Orthodox Judaism is defined as "Following the laws of the Bible (Torah) as interpreted by tradition and the Rabbis (i.e. the Talmud)". For example: The Bible tells us not to work on the 7th day, tradition tells us what is considered work. It must be stated that Orthodox Judaism is the only form of Judaism prevalent in the whole diaspora (maybe an argument to prove the authenticy of OJ tradition) and is therefore the official religion of the State of Israel. Despite the differences between the various groups, all Orthodox Jews remain as one religion, they can pray together, intermarry, Rabbis share Talmudic discourse and the Israeli Rabbinical Court is comprised of Rabbis of almost all sects within Orthodox Judaism (while a Reform Rabbi would never be allowed to join).
Orthodox Judaism is then divided into three major groups: ultra-Orthodox (Haredi), Modern Orthodox and Religious Zionist. While many Modern Orthodox are also Religious Zionist, they are two totally separate ideologies which should be understood on their own.
Ultra-Orthodox Jews (about 1.3 million in Israel + about 1 million abroad) are largely defined as a group that is sticking to social traditions and to stringencies in Talmudic law well beyond what is necessary in order to be a "Kosher" Jew. UOJs understand that, they basically explain themselves that they just enjoy practicing Judaism and that keeping social traditions is safeguarding their children from negative influences from the "outside" (in Israel this results in a unanimous anti-army-draft policy, even by the non-anti-Zionist majority - as long as they can't shape the army's culture according to their beliefs and customs, causing much political drama). UOJ can be from all geographic backgrounds and the "ultra" can be on many levels. UOJs from European descent are largely divided between the Chassidic and Yeshivish sects (too much to explain here). A small part of the UOJ community is anti-Zionist (about 10%, my estimate), believing that Zionism is against the Torah in its essence (see TrueTorahJews.org). However, most of them don't dream of doing anything with that belief besides maybe telling it to their children. A very small part of them (the "radicals") would go the extent of visiting and showing support to the Iranian leadership and Palestinian activists (in rare cases even terrorists) (google search "Neturei Karta"). Knowing the group from very close, I can attest that they don't represent anyone, i.e. everyone who believes in those visits takes actual part in it, so they are about a few 100 people (despite them saying that they represent millions...). But again they aren't practically "violent".
In Israel anti-Zionist UOJs are often protesting, not all of them - that would be about 100k people, rather groups of 10s, those protests often result in non-permitted roadblocking, etc. (google: Haredi violent riot / images). I don't recall anyone being intentionally wounded or killed by anti-zionist protesters, I doubt it ever happened. (unintended wounds did happen in recent history).
There are some very specific accounts of violence perpetuated by individual UOJs, not organized or supported by groups, one very tragic example is a 16y old girl who was killed by an Orthodox extremist at the Jerusalem pride parade a few years ago. Besides this I don't remember anything of that scale.
There is a very small (amount of followers drastically changing throughout the years between 10s to 100s) very secluded extremist cult called "Lev Tahor" - they have been accused of abusing their followers especially women and children (they are known for relocating around the globe, escaping authorities). (google "Lev Tahor").
Modern-Orthodox Jews generally believe that Orthodox Jews should adopt everything from the western culture that is not in direct contradiction to Jewish law. Their whole ideology is therefore moderate by nature, making it almost impossible to develop anti-social extremism from its essence.
Religious Zionists (about 1-1.5 million in Israel) believe that modern Zionism and the modern State of Israel are part of the Jewish religion. Most of them (about 70-80%, relying on Israeli election preferences) are more modern than the Ultra-Orthodox and are more involved with the Israeli secular society.
Despite the bad connotation the term "Religious Zionism" can develop in the minds of people who don't know the group (I imagine something like Crusades...), almost all of them are very peaceful people who would never harm any human. However, the majority of the "harmful" violence targeting Arabs (resulting in death or injury), are attributed to members of this group, despite being about 25 perpetrators in total - in the last 75 years. Sad to see how a group of 1.5 million people who denounce violence, are misjudged due to the actions of a few.
The term "Hilltop Youth" is more of a description of Religious Zionist hippie-like boys who live in the wilderness on the hills of Judea and Samaria (the West Bank), in an attempt to settle them. It's not an actual organization, it's a trend of bums. Almost all violence (mostly damage to property) against Arabs in the last few years have been attributed to those boys. They are mostly known for getting into fights with Arabs - almost never possible to know/prove who started the fight (the one fight I witnessed was of a boy delivering a powerful blow to an Arab who cursed and threatened him - you judge it). The Israeli police is also known to being very unfriendly to them - arresting boys for minor provocations. However, it's hard to prove that the majority of them are violent or that they are driven by religious extremism rather than by lowlifeness. I don't have an estimate of how many boys they are, I doubt anyone has, since it's not a closed club - you can join it and leave it without notifying anyone, and one can dress like them or even join them in their tents without doing anything violent.