-

Pillar says:

vlans:
  - id: 100
    network: 10.20.0.0
    netmask: 255.255.255.0
    prefix: 10.20.0
    gateway: 10.20.0.1
  - id: 101
    network: 10.21.0.0
    netmask: 255.255.255.0
    prefix: 10.21.0
    gateway: 10.21.0.1

Templated file says:
{%- for vlan in pillar['vlans'] %}
subnet {{ pillar[vlan.network] }} netmask {{ pillar[vlan.netmask] }} {
       option routers                  {{ pillar[vlan.gateway] }};
       option subnet-mask              {{ pillar[vlan.netmask] }};
       range {{ pillar[vlan.prefix] }}.200 {{ pillar[vlan.prefix] }}.240;
       default-lease-time 1200;
       max-lease-time 2400;
}
{%- endfor %}

Salt says:
          ID: /etc/dhcp/dhcpd.conf
    Function: file.managed
      Result: False
     Comment: Unable to manage file: Jinja variable 'dict' object has no attribute '10.20.0.0'; line 62

              ---
              [...]
              }

              {%- for vlan in pillar['vlans'] %}
              subnet {{ pillar[vlan.network] }} netmask {{ pillar[vlan.netmask] }} {
                     option routers                  {{ pillar[vlan.gateway] }};
                     option subnet-mask              {{ pillar[vlan.netmask] }};    <======================
                     default-lease-time 1200;
                     max-lease-time 2400;
              }
              {%- endfor %}
              ---
     Changes: