Hi Dirk,
As you are using IP-Helper on the SWITCH and not on the gateway, all you need to take care of in the rulebase is DHCP-Relay from switch to the DHCP server. This traffic will be sent by the switch on it's management interface to the DHCP server, so that is where you will need to see for the need of any rules.
If this is not passing through the Firewall, when the switch and DHCP server are in the same network, there is no need for any rules.
The SK is referring to the Firewall being the DHCP Relay server.
Regards, Maarten.
Regards, Maarten