@Gink OK the first step is to get it to boot on the same subnet. The next step is a bit harder. Its not so bad if you are using a MS/Linux DHCP server, with DNSMASQ the next process “might” work.
On your router between the vlans. You probably setup a dhcp-helper or what also called a dhcp-relay service. In that service configuration you would typically point that service towards your real dhcp server. Then the router knows where to send the dhcp requests it hears on other vlans. Now in this setup, add the fog server IP as the last device in your dhcp-relay service configuration. You still want your main dhcp server to provide the IP addresses for everything, just dnsmasq has to hear the request so it can reply correctly, otherwise the dnsmasq service is only listening for dhcp broadcasts on its local subnet. (understand this is just off the top of my head, but it sounds logical)