So the problem is that the Lenovo M5210 uses a LSI 3108 chipset, which is a RAID controller and not an HBA, as such has no means of flashing to 'IT Mode' for straight passthrough of the drives.
While you've forced it into JBOD, it's not HBA mode, and so doesn't provide the full access to the disks that Storage Spaces is expecting.
Your best option is to swap out the M5210 with a Lenovo N2215 SAS/SATA HBA for System x, which has a LSI 3008 HBA Chipset that's fully supported for Storage Spaces. The part number is 47C8675 and looking at ebay, they're ~$150.
And as for not needing 'microsoft approved' solutions, it's not about approval, it's about avoiding pain and suffering later on when doing maintenance and the likes.