This is a notoriously difficult subject for any RAID controller as the RAID chip masks the actual drives and only exposes the volume to the OS.
The only option I have found is to look in detail through the management software for your particular RAID controller. In there somewhere will be a menu to examine SMART status, which is invariably where they lump the drive temperature too.
Sorry I cannot be more specific as I never use onboard RAID as a plug in 3rd party card is always better, usually because of a dedicated RAID chip and some cache RAM.