Intel RSTe (Rapid Storage Technology) and Intel VROC (Virtual RAID on CPU) are firmware based RAID technologies, they setup the RAID on the firware/bios setup screens (similar to how true hardware RAID devices do) not by the OS.
Unlike true hardware RAID, these present to the OS as MD Raid Devices.  However because these present as pre-existing MD Raid devices the installer does not honor them.
I was told (see ticket  https://issues.redhat.com/browse/OCPBUGS-15436 ) that this is because CoreOS does not support hybrid raid devices. 

This needs to be addressed as customer who purchase systems with this technology will want to use it.

Please note that RHEL does fully support this, so there is no reason for CoreOS not to support it.