Markus,
I am working with the same server model as you. It wasn't until I changed the "AHCI Capable SATA Controller" to "ENHANCED" that my drives on the onboard SAS/SATA controller became visible to ESXi.
Do not set this to "COMPATIBILITY" mode because that will use PATA emulation and you will suffer a noticable decrease in performance.
It is strange because it feels like I am changing a setting that should have no effect on whether or not ESXi can detect my drives. I understand that it cannot support the RAID because it is technically a Software RAID, but as I saw (and you showed with your error logs) it appears to try and associate the "scsi-rste" driver and fails to do so when the setting I mentioned is in AHCI mode.
-Ben