Hi Mario,
The old hosts will still need to be used, and returned to the existing 4.1 vCenter once migration has completed.
The DRS comment was just for the new hosts as only one host has visibility of both exiting and new storage devices, that host was originally planned as a "proxy" to migrate between existing and new storage devices.I didn't want DRS try and vmotion VM's onto hosts that don't have visibility of the old storage.
Regards,
David