Can I use any storage device to store user profiles using Profile Manager?
I think what you are asking is how to enable (network) "Home Directories". Workstations need to be connected via Gigabit Ethernet for this to work well. For laptops, use "Portable Home Directories" over a robust Wi-Fi network (or Ethernet)

Yes, you can use any (direct-attched) storage device, though for 40TB, I would recommend a RAID over Thunderbolt (2 if possible).

In File Sharing, add or create a new shared folder on your external (direct-attached) storage, then click the check box to "Make available for home directories over... " and select a file sharing protocol (AFP or SMB).

Set up the Home Folder (directory) location in "mobility" using Profile Manager