The first argument to the combine filter must be a dictionary. You're calling:

  - set_fact:
      node_data: "{{ node_data | combine ( item.split(' ').0 : { 'name': item.split(' ').0 , 'ip' : item.split(' ').1 }, recursive=True) }}"
    with_items: "{{ nodes.stdout_lines }}"

You need to make that:

  - set_fact:
      node_data: "{{ node_data | combine ({item.split(' ').0 : { 'name': item.split(' ').0 , 'ip' : item.split(' ').1 }}, recursive=True) }}"
    with_items: "{{ nodes.stdout_lines }}"

Note the new {...} around your first argument to combine. You might want to consider reformatting this task for clarity, which might make this sort of issue more obvious:

    - set_fact:
        node_data: >-
          {{ node_data | combine ({
            item.split(' ').0: {
              'name': item.split(' ').0,
              'ip': item.split(' ').1
            },
          }, recursive=True) }}
      with_items: "{{ nodes.stdout_lines }}"

You could even make it a little more clear by moving the calls to item.split into a vars section, like this:

    - set_fact:
        node_data: >-
          {{ node_data | combine ({
            name: {
              'name': name,
              'ip': ip
            },
          }, recursive=True) }}
      vars:
        name: "{{ item.split(' ').0 }}"
        ip: "{{ item.split(' ').1 }}"
      with_items: "{{ nodes.stdout_lines }}"