Migration worked!
Please feel free to copy on Blogs, Wikis and so on!
There is a better way probably(Libvirt on another Server/Linux Workstation an import through KVM), but this just works.
=> How to Migrate VMs from Proxmox:
Requirements:
- Port 54322/tcp open on oVirt Hosts
- ovirt-imageio-daemon running on Hosts
- ovirt-imageio-proxy running on (Hosted)-Engine.
-- Attention: this will move disks through different Storages from Proxmox. --
1 - Add a Storage to Proxmox, like NFS or a local share.
2 - Click on a VM from Proxmox and choose the option "Move Disk" on the taskbar above.
3 - Choose qcow2 as a export file and save the file on the added storage.
4 - On oVirt-Engine go to Disks and click on Upload(Taskbar above) and add the size of disk from Proxmox( to check how big it is: on Proxmox through "Hardware" on the left sidebar from VM).
5 - Create a new VM and attach the qcow2 disk.
6 - Check the Network Configs, if you did something with udev-rules you will need to change the mac address.
Many Thanks to Gianluca and Nathanäel!
Best Regards,
Gabriel