Note that RHEV 3.5.z should support EL6, which has a considerably older libvirt version.
Not sure if this changes the solution, but at the very least it should be verified on both platforms.
Verified with
=============
rhevm-3.5.7-0.1.el6ev.noarch
vdsm-4.16.33-1.el7ev
libvirt-1.2.8-16.el7_1.5
Steps to Reproduce:
===================
1. Assign a Direct Lun to a VM with interface "Virtio-SCSI" and "Enable SCSI Pass-Through".
Works fine.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://rhn.redhat.com/errata/RHBA-2016-0317.html