NOTE: my response is entirely speculation, I don't know this for certain.

I believe it would technically be possible, but likely unsupported and definitely not recommended. Unfortunately I do not have a RHEVH host to look at (mine are all RHEL-Hypervisors) but if you login and look at some of the filesystems and Volumes that are present, you will see numerous items that are surprising (VGs and LVs with UUIDs for example). That makes me wonder if VDSM would be capable of handling md devices.

Have you considered using RHEL as your RHEV Hypervisor? (Does anyone else know if you can use RHEL as a Hypervisor and still use local storage as backing for Guests?)

Or, another possible solution: You could build a separate host (using MD, etc..) and share it out via NFS (or iSCSI) to your Hypervisor. That would allow for storage growth and simple guest migration down the road.