Format of Hard Drives in EX2 Ultra - is NTFS compatible?

Very unlikely; the MyCloud family uses an embedded Linux OS, and thus uses ext3 and ext4 Linux file systems.

You will be better off asking on the EX2 forum; this is for basic, single drive MyClouds.

You should also download and read the EX2 user manual; I’m sure it will explain how to install disks, and how to get them running, in whatever JBOD or RAID setup you want.