If you Roulette as a level 50 character you'll get Tomes. If you Roulette as a character that is level 50 in one class, and not yet level 50 in another, you won't get Tomes, because you'll get the additional EXP bonus.

Example: You have a level 50 ACN, but go into Low Level Duty Roulette with a level 23 CNJ, you won't get Tomes.