For anyone who stumbles upon this - I have managed to test this setup with VMs under KVM.
It seems that all 3 systems need to be oVirt Nodes, while my 3rd node has 1 CPU and 1GB of
RAM with 20GB of local storage - so most probably this setup is doable.
Still I need to test the HA once the host is down - the engine should be powered on
another host and GlusterFS should be still running.