Yes, forwarding can be configured by using a default forwarding sequence without forwarding layer of forwarding policy. Define a forwarding host and refer the alias from the Management Console: Configuration > Forwarding Hosts > Default Sequence > Selected Alias.
The default sequence will also be used when there is no matching forwarding rule in policy.
What happens if you don't select an alias?
If an alias is not selected then the traffic is only proxied and no forwarding is done.