Hi!
I have installed your check on my server, and it finds all disks and lists them in checkmk. To make sure it works, I connected a disk with SMART errors to a device and tested the script again, it still reports the disk to be fine.
I am managing linux servers too, and these use smartmontools which works fine. you can have smartmontools on windows x64 too, https://sourceforge.net/projects/smartmontools/ has a precompiled version.
My knowledge in powershell scripting is really small, is it possible to adopt the smart script from linux clients to windows and powershell? We would be able to see much more details about the disks.
Thank you for the scripts, they are a good starting point!