You don't want to do that. The Unraid spin down control will not understand the standby status of the disk then.
To properly spin down a UD disk, use the UD cli command and Unraid will keep the disk status up to date. Click the 'Help' icon to see the command,
I have found the contrary situation on my server. I cannot spin down a disk without a file system.
I'm looking into this.
The temperature display might be a UD issue, At a terminal type this command:
cat /usr/local/emhttp/state/devs.ini
This shows information on UD devices from Unraid's perspective. See it the temperature is shown and let me know if it is, but not shown on the UD page.