According to Intel's website, TRIM is not supported for any RAID configurations at the moment:
TRIM support in Windows 7 [and 8] (in AHCI and RAID mode [only] for drives not part of a RAID volume)
Source: http://www.intel.com/support/chipsets/imsm/sb/cs-022304.htm
That page is dated 04-Oct-2012, so pretty recent, too. Their latest SSD Toolbox FAQ supports this stance as well (see Q11).
Of course, Intel being Intel, this appears to be completely wrong, and they DO support TRIM in RAID 0 configurations (but only for 7 Series chipsets).
RST 11.2 supports TRIM on RAID 0 only on Intel Desktop Boards with the 7 Series chipsets.
Source: http://downloadcenter.intel.com/Detail_Desc.aspx?DwnldID=21407
And the following Anatech article details support for TRIM support in RAID 0:
The feature is limited to Intel 7 series chipsets with RST RAID support and currently only works on Windows 7 OSes, although Windows 8 support is forthcoming.
So it IS supported. Just not by Windows 8 at the moment.
Update: It appears Windows 8 RAID 0 TRIM is supported as of RST version 11.6.0.1030. Just make sure you install all the Windows 8 Updates before you unstall RST.
Good luck!