I have found also this topic:
"RHEV 3.5 supports both RHEL6 and RHEL7 hosts (RHEL or RHEV-H). It is recommended to
upgrade your hosts to RHEL7 once on RHEV 3.5."
If this is true i could make an update of the hypervisors 6 and not a reinstall with
centos 7 to reach the 3.5 release...After this as you suggest i can do a storage domain
detach from 3.5 in order to attach to a new 4.3 enviroment...