Please note that you will get degradation overtime using a Solid State Drive in a RAID array since the RAID software works with SCSI commands and the Solid State Drives works with SATA commands, therefore the solid drives cannot work with the SATA commands. If you want to get the TRIM command working natively you need to use the AHCI option or RAID but the Solid State Drive cannot be part of a RAID array and you need to use Windows* 7.
I have a similar chipset in a dedicated server (supermicro 5017C-TF with a X9SCM-F motherboard), which runs on a C204 PCH chipset.
Would the performance degradation still take place when making a (BIOS/hardware) RAID setup using modern SSDs (such as Intel 530 SSDs) which have builtin TRIM function in their own controllers?
Support for the TRIM functionality in SSD's under RAID systems depends on the the Storage controller, driver and Operating System.
For example, TRIM functionality for Intel SSD's and the Intel® C204 Chipset working in RAID mode, can run in RAID 0 using Intel® Rapid Storage Technology (Intel® RST) 11.0 or greater. NOTE: Trim on RAID 0 is not supported on Windows 8* or Windows Server 2012.
The Intel® Solid-State Drive 530 and other Intel SSD's have a "garbage collection" feature in the drive controller that runs in the background during IDLE times, however, TRIM is more efficient as it can run upon user request using Intel® SSD toolbox, or by the OS upon file deletion/modification.
If your configuration does not allow SATA TRIM commands, it is possible that the performance of your SSD degrades over time. If you notice this behavior, you may need to perform a Low level format (Secure Erase) to "zero" or "flush" the drive.
Please take into consideration that Intel Data Center SSDs have additional features that make them less susceptible to this condition.