I would suggest Hall of Novice completion should be mandatory requirement before you head into a Duty Finder for each role. Meaning that you need to finish Hall of Novice with the role in question before you are allowed to partake Duty Finder with that particular role.

Someone who has a lvl 80 dps would still need to do Hall of Novice for Tanks if they are to play a Tank job and use DF with it. Especially important for the Tanks that start at higher level.