First you ve to set Netork Setup Method in the Global settings tab to raditional with ifup/wicked. Else YaST assumes you will use NetworkManager and thus not offer any configuration options at all.
Then you must select the network card you want to use DHCP in from the list on the Oveview tab and click Edit below. On the page you will get then, you are able to choose Dynamic ddress using DHCP. Only then is DHCP switched on and only after that you can use the setting you mention above if you think you need that .