No! All projects need a variety of skills, coding is just one of the many.
Do I have to stay up the entire hackathon?
No! You and your team decide on goals and mini-goals. Outside of some defined checkpoints, your time is your own.
Is it a contest?
Sometimes, but if it is we clearly define the judging criteria. We do often enjoy a little healthy competition from small tasks to the overall judging of the final product with sponsor-provided prizes.
Will this interfere with me attending the conference or participating in a student program?
Though we can not speak for your schedule or associate responsibilities, we do work closely with conference organizers to not conflict with other events. Commonly this is why the hackathons take place during night hours or in the case of HPC in the City, the week prior to the conference.