Hey.
I've had this "problem". I believe there is no automatic and transparent way to do this, so I can say what I did:
- I installed the default kernel (full virtualized) on the VMs and set it as default.
- I exported the discs (OVA), unzipped them with tar
- I used qemu-img to convert the disks to qcow2
- I added the disks to a Domain Storage, in oVirt
- I recreated the VM using the previously added disk.
It is worth remembering that Xen Citrix uses paravirtualized drivers, so you may have to uninstall them first and/or install the paravirtualized kvm drivers.
Maybe, just maybe, you have to upload a temporary VM on a raw KVM using virt-manager, because maybe oVirt doesn't recognize the disks the first time. So I only managed to upload a VM using IDE type disks. After you adjust the drivers, you can safely use Virtio-SCSI type disks.
Hope this helps.