Yes. In cDOT each node must have root volume on dedicated aggregate.
8.3 introduced Advanced Disk Partitioning, where small part of each disk is used for root aggregate and the rest - for data. This leaves you with almost full disk capacity for data. Actually, this should be default on new installation - I am surprised you did not get it.
You must reinstall each node to use ADP. On your model when you go to Special Boot menu and select 4, in Data ONTAP 8.3 it will automatically partition all disks assigned to the controller into root and data parts and create root aggreate from root partitions. It makes sense to do "set-defaults" in loader prompt before. Root partition size is computed automatically based on number of disks, so be sure to perform assignment as need in maintenance mode before starting installation.