For the AP Spanish Language Exam, do you need to know the "Vosotros" tense?

I would think so, as it's apart of the language. You can look at past AP tests as well as asking students who took it, or asking a teacher.

I was in the same situation this past year, and yes, the exam is extremely hard. However, I managed to get a 4 on the exam after only taking Spanish IV Honors, and I had very little time to prepare or outside help. If you are naturally good at Spanish and willing to put in the hours to do well, you'll be fine. One of the things that helped me the most was listening to the radio in Spanish whenever I was in the car or any other time I normally had music on, because that really forces you to begin to understand a speaker regardless of rate. Television really helps, and finding synonyms for words and having a wide vocabulary will give you a better chance on the writing. It sounds like you have a really good chance at a 4 or a 5, in all honesty. Good luck to you!

In Spain and in the Spanish literature it's used. You should learn it because you don't know if you going to need in the future. Knowledge is power.

*I don't believe it is, but your best bet would be to ask a Spanish teacher at your school*