The RAID controller BIOS may need to be set. This is typically done by pressing a key during the initialization of the controller. Consult the documentation for the RAID controller for information on this.
Assuming that you have correctly configured the BIOS of the RAID controller, if the installation still sees the disks as separate devices, then the RAID controller is most likely a hybrid software / hardware RAID controller. These controllers rely on the operating system driver to provide the RAID functionality. In this case, it is not a true hardware RAID device.
For these types of controllers, to get the desired RAID functionality, use the software RAID driver provided with Red Hat Enterprise Linux, selecting RAID as the partitioning scheme during the installation process. The performance of this RAID functionality will be on par with the performance of the controller using its software drivers under other operating systems on the same hardware.