Yes, you would have to pay the first years tuition if you are not awarded a scholarship for that year. However if you get into an academy, the tuition to you, is free. With relation to tuition, the purpose for an ROTC scholarship is to pay for your college and the academies are already paid for.
If you accept an appointment to an academy, you are saying you are willing and committed to serving that branch for the required five years. Thus, if you don't like the branch but you get accepted to the academy, don't accept unless you want to serve in that branch.