It should be possible to create new hosts by importing an existing VM into Foreman. It could be done similar to the clone action of a host, but triggered from the VM listing in the compute resources show page. The attributes provided by the compute resource should be imported.

The use case is, that you might not be able to create your VM through Foreman (because of internal policies, special configuration needs, ...) but still want to use Foreman to install the VM.