Well, I just visited Jumpcut for the first time, and I will tell you right now: I would never allow students to browse the videos there. As I was clicking through the recently popular videos, one was deeply disturbing: scenes of self-mutilation and drug use, and who knows what came after I stopped it. There were no indications that what I was about to see might be inappropriate for some audiences, no descriptions listed, and the tags visible without scrolling down gave no indication either. Scrolling down in shock, some more tags listed "horror" and "addiction:" now I know to check.
I will go back and explore this site a bit more, but to be frank, Jumpcut will have to have some pretty amazing tools for me to get over this unfortunate experience. And even if the tools are useful, I would be very hesitant to use them in a school setting: this site is NOT student safe.