lookup.j2

{% for host in groups['gluster_servers'] %}
{% if host != inventory_hostname %}
  {% if 'ansible_' + rhel7_interface in hostvars[host] %}
  - {{ hostvars[host]['ansible_' + rhel7_interface]['ipv4']['address'] }}
  {% else %}
  - {{ hostvars[host]['ansible_' + default_interface]['ipv4']['address'] }}
  {% endif %}
{% endif %}
{% endfor %}

play.yml

---
- hosts: gluster_servers
  vars: 
    rhel7_interface: enp0s3
    default_interface: eth0
  tasks:
    - set_fact:
        other_servers: "{{ lookup('template', 'lookup.j2') | from_yaml }}"
        
    - debug:
        msg: "addresses to use: {{ other_servers | join(',') }}"