Ansible command with_items

I think you can register the result to a variable, then print with debug.

- name: print to stdout
  command: echo "hello"
  register: hello

- debug: msg="{{ hello.stdout }}"

- debug: msg="{{ hello.stderr }}"

From what you're asking, it sounds like you just want to specify the vhosts group as the hosts to run a specific role on. So your playbook should start something like this:

---
- hosts: vhosts
  name: Tasks run on vhosts
  roles:
    - { role: somerole }

Keep in mind that you can have multiple plays in your playbook, so it's perfectly fine to do something like this:

---
- hosts: all
  name: Run roles for all servers
  roles:
    - { role: role1 }
    - { role: role2 }
    - etc.

- hosts: vhosts
  name: Run roles specific to vhosts
  roles:
    - { role: vhost-role }

- hosts: all
  name: Post-vhost roles for all servers
  roles:
    - { role: role3 }
    - etc.

If you have a single playbook that you want to run on different host groups at different times then you can use a variable for the hosts entry:

---
- hosts: "{{ somevar }}"
  name: Run roles against a user specified set of hosts
  roles:
    - { role: foo }

And then you'd invoke this last one in one of these ways:

$ ansible-playbook playbook.yml --extra-vars "somevar=vhosts"

$ ansible-playbook playbook.yml --extra-vars "somevar=host1,host2"