Using foreman-1.5.1 and oVirt-3.4.2 there is no VM listing while in a oVirt CR. There is an error instead: undefined method `[]' for nil:NilClass.
Enabling debug and commenting out a couple of lines in app/controllers/compute_resources_vms_controller.rb I got a stack trace pointing to rbovirt.
Injecting some debug log statements into various files of rbovirt I have found the problem.
My Test-oVirt CR doesn't have iscsi direct luns but Prod-oVirt has and volume.rb errors out when encountering a direct lun disk. My current solution is to add a few 'rescue nil' entries to a couple of lines but that might only stop the error. Could have unknown side effects.
See email on foreman ML topic: Problem with showing VMs with foreman-1.5.1 and oVirt-3.4.2