I'm not overtly familiar with how RHEV works, and not too into the workings of OVF tool.
Converter can take a live Linux OS and produce a VM inside of vSphere (at least last I checked). you could point to the RHEV VM's IP and see if it'll work, send it to vSphere (vCenter), then import to vCloud from there.
Otherwise, I'd ask in the converter forums to see if anyone has gone from RHEV to vSphere using converter.