There exists a bug in the Yast firewall scripts for configuring access to a DHCP server. DHCP requires broadcasting capability but the Yast firewall script does not enable this by default. In order to fix the problem ensure the following two directives are set in the /etc/sysconfig/SuSEfirewall2 script:
FW_SERVICES_EXT_UDP="bootps"
FW_ALLOW_FW_BROADCAST="yes bootps"
Setting these two directives will allow the DHCP server to broadcast its availability to the rest of the network without having to lower your server's firewall.