Difference between and RHEV & Ovirt
RHEV is the stable version, while oVirt is upstream.
Features from oVirt get merged into RHEV when stable and tested.
Consider Fedora and RHEL - Fedora is a rich distribution in terms of features and packages, but it's not supported commercially, has a short lifecycle, and is not geared towards stability. RHEL is based on Fedora, but it's code is tested and stabilized.
Same goes for oVirt - it's a bleeding edge development, off of which RHEV is based. oVirt is very new, but not as stable as RHEV, and has no commercial support. RHEV is not as advanced, but it's stable, well tested and geared towards the enterprise and mission critical systems.
To know more about Ovirt Click Here
For RHEV Click Here