RHEL/CentOS uses a dracut system. By default, dracut-initramfs does not include a qemu driver, this may be one of the possible reasons why the machine doesn't boot.
Execute the following command on the source machine:
# sudo dracut -N --regenerate-all --force
This command will regenerate core hardware drivers for all installed kernels.
If this doesn't help, please contact support@hystax.com