FWIW, I just removed all drive letters from my DrivePool HDDs. DrivePool does not need a drive letter to recognize a HDD in the pool. It uses the hidden PoolPart directory.
Removing drive letters on the HDDs makes a less cluttered display in Windows 10 File Explorer as it will only show HDDs with drive letters. That works great for me as I currently have 16 HDDs in my DrivePool. Those HDDs are dedicated to DrivePool and nothing else. So I don't need any drive letters assigned to them.
Of course, when you remove the drive letters, Windows 10 File Explorer can longer "see" the drive normally. You would have to go back into Disk Management and reassign a drive letter.
I track all my pool HDDs by name, such as DP01, DP02, DP03, etc.... which also corresponds to the physical location on my rack. I also put the drive name sticker on the physical drive/case for easy identification. The HDDs in my pool do not have drive letters assigned to them, as I stated. The DrivePool UI lists the names all in alphabetic order, which is very nice. However, if for some reason I want to reassign a drive letter to a particular drive, I just use Disk Management and look up the HDD by name. That is much easier then trying to track all the S/N of the HDDs.
I am not using Scanner, so I am not sure if that program requires drive letters to work. Is there some reason you need/want to keep any drive letters assigned to your pool HDDs? I found DrivePool was easier to work with when I removed all those drive letters from my pool HDDs. Just my thoughts to your initial question on how to not drive yourself crazy with numerous drives in DrivePool.